HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Figures Only Full Text (PDF) Services Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (13) Citing Articles via Google Scholar Google Scholar Articles by Ghezzi, E.M. Articles by Ship, J.A. Search for Related Content PubMed PubMed Citation Articles by Ghezzi, E.M. Articles by Ship, J.A.

Aging and Secretory Reserve Capacity of Major Salivary Glands

¹ University of Michigan School of Dentistry, Department of Cariology, Restorative Sciences, and Endodontics, Ann Arbor;
² New York University College of Dentistry, Department of Oral Medicine, and Bluestone Center for Clinical Research, 421 First Avenue, 2nd Floor, New York, NY 10010-4086, USA;

*corresponding author, jonathan.ship{at}nyu.edu

	ABSTRACT

TOP ABSTRACT INTRODUCTION METHODS RESULTS DISCUSSION REFERENCES

 
A loss of acinar cells occurs with aging, while salivary production remains age-stable in healthy adults. It is hypothesized that a secretory reserve exists to preserve function despite a loss of acinar cells in normal aging. The purpose of this double-blind, placebo-controlled, crossover study was to determine age-related differences in salivary response to an anti-sialogogue (glycopyrrolate). Thirty-six healthy subjects (18 young - 20-38 yrs; 18 older - 60-77 yrs) received 4.0 µg/kg IV glycopyrrolate. Parotid and submandibular/sublingual saliva samples and xerostomia questionnaire responses were collected. Variables calculated for each subject were: times to initial and maximum suppression and xerostomic complaint; time to recovery; and durations of suppression and complaint. Salivary function was more adversely affected in older persons. There were no consistent age-associated questionnaire response differences. These findings suggest that salivary gland output is more adversely affected by an anti-sialogogue in healthy older vs. younger adults, supporting the secretory reserve hypothesis of salivary function.

KEY WORDS: aging • reserve • saliva • parotid • submandibular/sublingual • xerostomia

	INTRODUCTION

TOP ABSTRACT INTRODUCTION METHODS RESULTS DISCUSSION REFERENCES

 
Organ reserve is the difference between basal and maximum organ function (Montgomery, 2000), and has been demonstrated in biologic systems such as the heart, lungs, liver, and kidney (Epstein, 1996; Saltzman and Russell, 1998; Schmucker, 1998; Janssens et al., 1999). Gradual loss of reserve capacity is considered normal physiologic aging (Fries, 1980), yet age-related structural changes do not necessarily affect organ function in healthy individuals. Histomorphometric examination of "normal" salivary gland tissue revealed age-associated decreases in the number of acinar cells (Scott et al., 1987), while salivary production remains age-stable in healthy, non-medicated adults (e.g., Ship et al., 1995; Ghezzi et al., 2000). Accordingly, a secretory reserve in salivary glands has been hypothesized to account for loss of cells in normal aging in the presence of preserved functional capacity in older adults (Scott et al., 1987; Baum et al., 1992).

Physiologically stressful circumstances (disease, surgery, radiotherapy, pharmacotherapeutics) can strain the reserve capacity, thus hindering its ability to compensate for increased metabolic demand and resulting in compromised function (Evers et al., 1994). Identification of normal physiologic age-associated changes is critical in differentiation between normal functional decline and disease in aging (Fozard et al., 1990). If normal aging and reserve capacity are understood, vulnerable populations at risk for impaired organ function and failure can be identified.

Many older adults complain of a dry mouth and experience the deleterious consequences of salivary hypofunction (e.g., Närhi et al., 1999; Thomson et al., 1999). Accordingly, the "normal" aging process has been suggested as an etiological factor for salivary dysfunction (Pedersen et al., 1985; Cowman et al., 1994; Yeh et al., 1998). However, prospective and longitudinal studies demonstrate that salivary gland function is age-stable in healthy adults (e.g., Ship et al., 1995; Ghezzi et al., 2000). Salivary dysfunction in older adults is likely due to systemic diseases, prescription and non-prescription medications, chemotherapy, and head and neck radiation (e.g., Ship et al., 2002).

Salivary glands are readily accessible and well-characterized; therefore, they are a useful tool for the study of the normal aging process and the impact of stress (e.g., medication use) on organ reserve and secretory function (Baum et al., 1992). As the number of acinar cells decreases with age, the adverse effects of anticholinergic drugs on salivary output should become more pronounced. However, to our knowledge, no studies have investigated this phenomenon.

The purpose of this study was to utilize salivary glands to examine the influence of aging and secretory reserve in an organ system. We assessed the existence of reserve capacity of salivary function in healthy adults by investigating age-related differences in salivary responses following administration of an anticholinergic drug (glycopyrrolate). It was hypothesized that after administration of glycopyrrolate, older adults would experience greater salivary hypofunction compared with younger adults.

	METHODS

TOP ABSTRACT INTRODUCTION METHODS RESULTS DISCUSSION REFERENCES

 
Subjects
Study participants were 18 young (20-38 yrs; 24.3 ± 3.8, mean ± SD) and 18 older healthy adults (60-77 yrs; 69.9 + 5.1) of middle socio-economic class, diverse racial background, and equally distributed by gender. Each subject was given a complete physical exam and treadmill test. Ineligibility included: (1) evidence of provokable angina or ECG changes during the treadmill test; (2) treatment for systemic diseases; (3) pregnancy; (4) resting ECG abnormality; (5) prescription or non-prescription medication intake associated with salivary hypofunction within 7 days; or (6) history of head and neck radiotherapy or salivary gland hypofunction or disease.

Study Design
This randomized, double-blind, placebo-controlled, crossover design study consisted of three visits at the University of Michigan General Clinical Research Center. At the first visit, each subject signed a University of Michigan IRB-approved informed consent. Each subject received a physical exam by the medical staff and underwent a treadmill and cardiology test to rule out significant cardiovascular disease.

At the second and third visits, the study protocol was identical with the exception that participants were randomly assigned to receive a 4.0 µg/kg dose of intravenous (IV) glycopyrrolate or IV placebo (5% dextrose in water, D5W), alternately. No statistically significant sequence effect was detected based on the visit order in which drug and placebo were administered. Both subject and examiner were blinded to the drug status of the subject.

Participants were not allowed to eat, drink, perform oral hygiene, or smoke 1 hr prior to the study. Upon entry into the study, all participants emptied their bladders and were weighed. Starting at the second hour, subjects received 20 mL of IV D5W each hour. Subjects refrained from exercise or strenuous activity, eating, and wearing removable dental prostheses, but were free to use the bathroom facilities for the six-hour study duration. Continuous ECG monitoring was performed throughout the study so that cardiac changes could be assessed; however, no observable alterations in blood pressure and pulse rates occurred following glycopyrrolate administration.

At baseline (collection time #1; CT 1), sitting blood pressure and pulse rate were measured, parotid and submandibular/sublingual saliva samples were collected (see below), a xerostomia questionnaire was administered (see below), and blood was drawn (see below). Following IV administration of 4.0 µg/kg glycopyrrolate or placebo, these measures were collected every 10 min for the first hour (CT 2-6), 15 min for the second hour (CT 7-10), 30 min for the third hour (CT 11-12), and then every hour until the end of the sixth hour (CT 13-16). Following the study, participants emptied their bladders and were weighed. Normal urinary function was demonstrated prior to discharge.

Drug
Glycopyrrolate, a muscarinic receptor antagonist used to inhibit salivation prior to induction of anesthesia, was chosen for this study (Ali-Melkkila et al., 1989). Dryness of the mouth persists for 24 hrs after oral intake and 8 hrs after intravenous and intramuscular administration of glycopyrrolate. Unlike other anticholinergic drugs, glycopyrrolate does not cross the blood-brain barrier, has a rapid onset of action, short half-life, and strong specificity for salivary glands. Glycopyrrolate causes less heart rate elevation and lower dysrhythmia incidence compared with other anticholinergic medications (Ali-Melkkila et al., 1991). The glycopyrrolate onset of action is within 1 min of IV administration, and it is rapidly cleared from the blood stream (Ali-Melkkila et al., 1989, 1991).

Parotid and Submandibular/Sublingual Saliva Collection
Eight investigators were trained in salivary collection methods by the principal investigator (JAS) prior to study initiation. ANOVA tests used to determine investigator variation in saliva collection found no significant differences (p > 0.05) for stimulated parotid (SPFR) or stimulated submandibular/sublingual (SSFR) flow rates. Salivary samples were collected in an identical manner at the 16 CT. The study started at 8:00 am to avoid circadian variations in salivary flow rates (Dawes, 1972).

Unstimulated and 2% citrate-stimulated salivary collection methods have been previously described (Ship et al., 1995). Parotid saliva was collected for 2 min with a modified Carlson-Crittenden cup from one gland (Stone Machine Co., Colton, CA, USA), followed by a two-minute collection of submandibular/sublingual saliva by light suction; all samples were collected in pre-weighed plastic graduated conical tubes. Output of saliva was determined gravimetrically and reported as mL/min per gland.

Xerostomic Questionnaire
An eight-item, validated, Visual Analogue Scale (VAS) xerostomia questionnaire (Pai et al., 2001) was administered at the 16 CT. A higher VAS value corresponded to an increased complaint.

Blood Collection and Analysis
A 5-mL blood sample was collected at the 16 CT, centrifuged, aliquoted, and frozen at -80°C within 20 min of collection until batch analysis. A qualitative ELISA for the determination of circulating levels of glycopyrrolate in human plasma was developed by modifications to an ELISA designed to detect glycopyrrolate in horse urine (Neogen Corporation, Lexington, KY, USA). Color development within the wells was read and converted to glycopyrrolate concentrations (Statistical Ligand Immunoassay Analysis 2.04.07ad; Brendan Scientific Corp., Grosse Pointe Farms, MI, USA).

After IV administration, maximum glycopyrrolate concentrations were reached in 10 min, followed by a rapid decrease to a minimal concentration detected after 120 min, and below detectable levels after 240 min. No age- or gender-related differences were detected at any time point.

Statistical Analysis
Data were entered and analyzed with SAS software (Version 8.0, SAS Institute Inc., Cary, NC, USA). SPFR, SSFR, and VAS values did not follow normal distributions. Logarithmic transformation achieved normality and was used in all analyses for SPFR and SSFR (Neter et al., 1990). We created pooled placebo means for each subject by averaging the 16 placebo visit and the baseline glycopyrrolate visit values. We calculated pooled standard deviations by taking the square roots of the weighted means of the variance for each individual.

For each person, lower tolerance limits for SPFR and SSFR were calculated as the value 2.4 standard deviations below the pooled placebo mean for that subject (Fig. 1) (Schork and Remington, 2000). An upper tolerance limit for each of the 8 xerostomia questions was calculated as the value 1.8 times the interquartile range above the pooled placebo mean.

View larger version (18K): [in this window] [in a new window]   Figure 1. Stimulated submandibular/sublingual flow rates over a six-hour period of time in a healthy 24-year-old male after IV glycopyrrolate (4.0 µg/kg) and placebo (D5W). A, Start of suppression; B, Maximum salivary reduction; C, Recovery; A - C, Time of suppression.

1. Salivary suppression: SPFR or SSFR value below the tolerance limit (A); xerostomic complaint: VAS value exceeding the tolerance limit.
   
2. Maximum suppression: lowest SPFR or SSFR value below the tolerance limit (B); maximum complaint: highest VAS value above the tolerance limit.
   
3. Time to recovery: time (min) the SPFR or SSFR value was at or above the tolerance limit following suppression (C) or the VAS value returned to or descended below the tolerance limit following complaint.
   

Eight outcome variables were calculated for each subject from each of the SPFR, SSFR, and 8 VAS values:

1. pooled placebo mean (PPM; mL/min per gland or VAS value)
   
2. time to initial suppression or complaint (TIS; TIC; 0 to A; min)
   
3. time to maximum suppression or complaint (TMS; TMC; 0 to B; min)
   
4. maximum suppression or complaint (MS; MC; mL/min per gland or VAS value; B)
   
5. time to recovery (TR; 0 to C; min)
   
6. total duration of suppression or complaint (TS; TC; A to C; min)
   
7. number of subjects without suppression or complaint during study (NS: never suppressed)
   
8. number of subjects with suppression or complaint at CT 16 (NR: never recovered).
   

Comparisons between the age and gender groups were performed by Wilcoxon Rank Sum tests (outcomes 1-6) and Fischer’s Exact tests (outcomes 7-8). Statistical significance was defined as p < 0.0063 (0.05/8; 8 age group and 8 gender group comparisons for SPFR, SSFR, and xerostomia questions) when Bonferroni adjustment was applied to account for multiple comparisons.

	RESULTS

TOP ABSTRACT INTRODUCTION METHODS RESULTS DISCUSSION REFERENCES

 
No statistically significant age or gender differences in pooled placebo mean values were demonstrated for SPFR, SSFR, and the xerostomia responses.

For SPFR and SSFR, age and gender comparisons of outcome variables 1-8 were performed. The older group had significantly greater TR and TS (SPFR), shorter TIS (SSFR), and lower MS (SSFR) (Table; Fig. 2). Older adults also demonstrated a trend for lower MS (SPFR), shorter TMS (SSFR), and greater TR and TS (SSFR). All subjects were suppressed for SSFR.

View larger version (18K): [in this window] [in a new window]   Figure 2. Stimulated parotid flow rates over a six-hour period of time in 18 healthy young (ages 20-38) and 18 healthy older (ages 60-77) adults after IV glycopyrrolate administration. Results expressed as mean values ± SEM.

For xerostomia responses, age and gender comparisons of outcome variables 1-8 were performed. There were no consistent age or gender effects. Of all the xerostomia questions, statistically significant differences were found only for dryness of mouth and throat, where females had greater TR and more persons NR (data not shown). The results were not different when age group comparisons were adjusted by gender or when gender comparisons were adjusted by age group. There were no significant interactions between age and gender for all comparisons (data not shown).

	DISCUSSION

TOP ABSTRACT INTRODUCTION METHODS RESULTS DISCUSSION REFERENCES

 
This investigation demonstrated that major salivary gland output in healthy older adults is more adversely affected by an anticholinergic drug than that in younger adults. A salivary gland secretory reserve has been proposed to explain the loss of cells in normal aging (Scott et al., 1987) in the presence of preserved functional capacity in older adults (Ship and Baum, 1990; Ship et al., 1995; Ghezzi et al., 2000). In normal circumstances, lack of secretory reserve in older adults would not cause impaired function. However, conditions that adversely affect salivary function (i.e., anticholinergic medications) would cause greater impairment in an older compared with a younger person (Baum et al., 1992).

A gradual loss of reserve capacity has been considered "normal" physiologic aging. In health, reserve capacity permits homeostasis to occur by using a fraction of total organ functional capacity (DiGiovanna, 1994). Cardiopulmonary, hepatic, and renal reserves are reduced in the elderly, but do not necessarily impair organ function in healthy older persons. Adequate functional capacity can be maintained in the presence of non-pathologic, "normal" aging changes, but these organs are vulnerable to external insults (Fozard et al., 1990; Baum et al., 1992).

Physiologically stressful circumstances (e.g., disease, surgery, pharmacotherapeutics) strain the reserve capacity, thus hindering its ability to compensate for increased metabolic demand, resulting in compromised function (Evers et al., 1994). With increased susceptibility to acute and chronic stress, functional decline occurs more quickly and recovery takes longer in the older population. Salivary glands are ideal for demonstrating organ reserve capacity, since these exocrine glands are readily accessible, well-characterized, and reflect many systemic conditions (e.g., poorly controlled diabetes, HIV immunosuppression) (e.g., Atkinson and Wu, 1994).

In juxtaposition to the flow rate findings, the magnitude of xerostomic complaints was not significantly different between the age groups, thus corroborating previous studies that reported fewer complaints of xerostomia in older adults after dehydration (Ship and Fischer, 1997). This may represent a significant problem for older adults, since they may experience impairments in the ability to respond to acute and chronic insults to salivary function.

Further research is needed to determine whether lost reserve capacity results from "normal" aging in healthy persons or aging in the presence of pathoses. In addition, determination of possible alterations in the muscarinic receptor function in salivary glands of elderly people, as demonstrated in animal models (Maki et al., 1989; Olsen et al., 1997), needs to be investigated. However, results from this and previous studies utilizing healthy adults across the human lifespan (Epstein, 1996; Saltzman and Russell, 1998; Schmucker, 1998; Janssens et al., 1999) suggest that diminished reserve capacity is an age-dependent event.

	ACKNOWLEDGMENTS

Received October 17, 2002; Last revision July 3, 2003; Accepted July 25, 2003

	REFERENCES

TOP ABSTRACT INTRODUCTION METHODS RESULTS DISCUSSION REFERENCES

 
Ali-Melkkila T, Kaila T, Kanto J (1989). Glycopyrrolate: pharmacokinetics and some pharmacodynamic findings. Acta Anaesthesiol Scand 33:513–517.[ISI][Medline]

Ali-Melkkila T, Kaila T, Antila K, Halkola L, Iisalo E (1991). Effects of glycopyrrolate and atropine on heart rate variability. Acta Anaesthesiol Scand 35:436–441.[ISI][Medline]

Atkinson JC, Wu AJ (1994). Salivary gland dysfunction: causes, symptoms, treatment. J Am Dent Assoc 125:409–416.[Abstract]

Baum BJ, Ship JA, Wu AJ (1992). Salivary gland function and aging: a model for studying the interaction of aging and systemic disease. Crit Rev Oral Biol Med 4:53–64.[Abstract/Free Full Text]

Cowman RA, Frisch M, Lasseter CJ, Scarpace PJ (1994). Effects of beta-adrenergic antagonists on salivary secretory function in individuals of different ages. J Gerontol 49:B208–B214.[ISI][Medline]

Dawes C (1972). Circadian rhythms in human salivary flow rate and composition. J Physiol 220:529–545.[Abstract/Free Full Text]

DiGiovanna AG, editor (1994). Introduction. In: Human aging: biological perspectives. New York: McGraw-Hill, Inc., p. 9.

Epstein M (1996). Aging and the kidney. J Am Soc Nephrol 7:1106–1122.[Abstract]

Evers BM, Townsend CM Jr, Thompson JC (1994). Organ physiology of aging. Surg Clin North Am 74:23–39.[ISI][Medline]

Fozard JL, Metter EJ, Brant LJ (1990). Next steps in describing aging and disease in longitudinal studies. J Gerontol 45:116–127.

Fries JF (1980). Aging, natural death, and the compression of morbidity. N Engl J Med 303:130–135.[Abstract]

Ghezzi EM, Wagner-Lange LA, Schork MA, Metter EJ, Baum BJ, Streckfus CF, et al. (2000). Longitudinal influence of age, menopause, hormone replacement therapy, and other medications on parotid flow rates in healthy women. J Gerontol A Biol Sci Med Sci 55:M34–M42.[Abstract]

Janssens JP, Pache JC, Nicod LP (1999). Physiological changes in respiratory function associated with ageing. Eur Respir J 13:197–205.[Abstract]

Maki T, Kowatch MA, Baum BJ, Ambudkar IS, Roth GS (1989). Evidence for an alteration in the microsomal Ca2+ release mechanism in senescent rat parotid acinar cells. Biochim Biophys Acta 1014:73–77.[Medline]

Montgomery H (2000). Cardiac reserve: linking physiology and genetics. Intensive Care Med 26(Suppl 1):S137–S144.

Närhi TO, Meurman JH, Ainamo A (1999). Xerostomia and hyposalivation: causes, consequences and treatment in the elderly. Drugs Aging 15:103–116.[ISI][Medline]

Neter J, Wasserman W, Kutner MH (1990). Applied linear statistical models. Boston: Irwin.

Olsen JG, Salih MA, Harrison JL, Herrera I, Luther MF, Kalu DN, et al. (1997). Modulation by food restriction of intracellular calcium signaling in parotid acinar cells of aging Fischer 344 rats. J Gerontol A Biol Sci Med Sci 52:B152–B158.[Abstract]

Pai S, Ghezzi EM, Ship JA (2001). Development of a Visual Analogue Scale questionnaire for subjective assessment of salivary dysfunction. Oral Surg Oral Med Oral Path Oral Radiol Endod 91:311–316.

Pedersen W, Schubert M, Izutsu K, Mersai T, Truelove E (1985). Age-dependent decreases in human submandibular gland flow rates as measured under resting and post-stimulation conditions. J Dent Res 64:822–825.[Abstract/Free Full Text]

Saltzman JR, Russell RM (1998). The aging gut. Nutritional issues. Gastroenterol Clin North Am 27:309–324.[ISI][Medline]

Schmucker DL (1998). Aging and the liver: an update. J Gerontol A Biol Sci Med Sci 53:B315–B320.

Schork MA, Remington RD (2000). Tolerance limits. In: Statistics with applications to the biological and health sciences. Upper Saddle River, NJ: Prentice-Hall, pp. 157-158.

Scott J, Flower EA, Burns J (1987). A quantitative study of histological changes in the human parotid gland occurring with adult age. J Oral Pathol 16:505–510.[ISI][Medline]

Ship JA, Baum BJ (1990). Is reduced salivary flow normal in old people? Lancet 336:1507.

Ship JA, Nolan NE, Puckett SA (1995). Longitudinal analysis of parotid and submandibular salivary flow rates in healthy, different-aged adults. J Gerontol A Biol Sci Med Sci 50:M285–M289.[Abstract]

Ship JA, Fischer DJ (1997). The relationship between dehydration and parotid salivary gland function in young and older healthy adults. J Gerontol A Biol Sci Med Sci 52:M310–M319.[Abstract]

Ship JA, Pillemer SR, Baum BJ (2002). Xerostomia and the geriatric patient. J Am Geriatr Soc 50:535–543.[ISI][Medline]

Thomson WM, Chalmers JM, Spencer AJ, Ketabi M (1999). The occurrence of xerostomia and salivary gland hypofunction in a population-based sample of older South Australians. Spec Care Dentist 19:20–23.[Medline]

Yeh CK, Johnson DA, Dodds MW (1998). Impact of aging on human salivary gland function: a community-based study. Aging (Milano) 10:421–428.[Medline]

This article has been cited by other articles:

				M. D. Turner and J. A. Ship Dry Mouth and Its Effects on the Oral Health of Elderly People J Am Dent Assoc, September 1, 2007; 138(suppl_1): 15S - 20S. [Abstract] [Full Text] [PDF]

This Article Abstract Figures Only Full Text (PDF) Services Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (13) Citing Articles via Google Scholar Google Scholar Articles by Ghezzi, E.M. Articles by Ship, J.A. Search for Related Content PubMed PubMed Citation Articles by Ghezzi, E.M. Articles by Ship, J.A.