AGING AFFECTS MORPHOLOGY BUT NOT STIMULATED SECRETION OF SALIVA IN RATS

T.J. Lasisi1,2, S.T. Shittu1, M.M. Oguntokun1 and N.A. Tiamiyu1

  1. Department of Physiology, College of Medicine, University of Ibadan, Ibadan, Nigeria.
  2. Department of Oral Pathology, College of Medicine, University of Ibadan, Ibadan, Nigeria.

Abstract

Background: The role of aging on the salivary gland function still remains controversial and inconclusive. This study was undertaken to determine the effects of aging on the morphology and secretion of salivary glands using male Wistar rats.

Method: There were three age groups; group A (3 months old; n = 8), group
B (6 months old; n = 8), and group C (9 months old; n = 8). Body weights,
salivary gland weights, salivary flow rates, pH and salivary levels of sodium, potassium, calcium, chloride, bicarbonate, phosphate and total protein were measured and compared. Hematoxylin-eosin stained histological slides of the salivary glands were assessed for morphological changes.

Results: Body weights increased with age while mean parotid gland weight
was significantly higher in group B than in groups A and C. Mean salivary
flow rate was significantly higher in group B and C than in group A, and
mean salivary pH was significantly higher in group B and C than group A.
Analysis of salivary electrolytes and total protein showed that mean levels of sodium, potassium and bicarbonate increased with age significantly while mean levels of calcium, chloride, phosphate and total protein did not show significant change among the groups.

Conclusion: These findings showed that varying changes were observed in
the morphology of salivary glands of aging rats without impaired function.

Keywords: Aging, Salivary Glands, Salivary flow rates, Salivary electrolytes, Salivary total protein

Correspondence:

Dr Taye J. Lasisi
Department of Physiology,
College of Medicine,
University of Ibadan,
Ibadan, Nigeria.
E mail: jameelahlasisi@yahoo.com
Mobile phone: +2348053513471

Introduction

Saliva is a watery fluid secreted by the salivary glands. Salivary fluid is an exocrine secretion consisting of approximately 99% water and a variety of electrolytes and proteins. The components interact and are responsible for the various functions attributed to saliva1. The physiological functions of saliva include initial food digestion, taste perception, maintenance of tooth integrity, oral clearance, lubrication, and protection of the oral cavity against infections. At present, saliva represents an increasingly useful auxiliary means of diagnosis and the salivary glands of rats and other rodents have been used extensively over the past years as models for the study of physiological and biochemical processes associated with secretion of saliva2,3. An interesting and useful characteristic of rat salivary glands is that they are essentially undeveloped at birth but undergo progressive development into mature organs during the first few weeks of life4. This also makes them useful models for the study of the developmental aspects of the secretory functions of the salivary glands.

Aging is a normal physiological phenomenon that affects almost all organs including the salivary glands5. Age related changes in the salivary glands have been documented in humans6-8 and animals9-11 with varying results. However, it has not been fully determined how aging influences the biochemical composition of saliva. Some functional studies on healthy individuals showed that aging does not diminish the ability of salivary glands to produce saliva12,13. On the other hand, some studies reported that there might be a progressive, but minor reduction, in flow of saliva from the glands due to aging14,15. Furthermore, the effects of aging on biochemical composition of saliva are not clear; therefore, the aim of this study was to evaluate age related changes in the salivary glands histopathology and secretion in male Wister rats, and to add to available
information for preclinical experimental research on age-related changes in the composition of saliva.

METHODS
Experimental Animals
Twenty four five weeks old 24 male Wistar rats were purchased from the Animal Research House of the College of Medicine, University of Ibadan, Ibadan, Nigeria for the study. The animals were housed in a temperature, humidity, and light controlled environment on a standard diet with free access to water. They were randomly allocated to three groups groups A, B and C) and used for the experiment at different ages. Group A (the young group, 3 months old, n = 8), group B (the adult group, 6 months old, n = 8) and group C (the old group, 9 months old, n = 8) had their evaluations at 3, 6 and 9 months old respectively. All experiments were carried out in accordance with The Code of Ethics of the EU Directive 2010/63/EU for animal experiments.

Measurements of rat body weight, salivary gland weight, salivary
flow rate and pH
The rats were weighed using weighing balance (Citizen Scales, Mubai, India) and anesthetized with an intraperitoneal (i.p.) injection of ketamine (75 mg/kg). Each rat was positioned laterally after stimulation with pilocarpine (10 mg/kg, i.p.). Saliva was collected by free flow into sterile plain tubes for a period of 10 minutes for each animal. To reduce the effects of diurnal variation, saliva was collected between 8 and 10 am for all the groups. Salivary flow rate (ml/min) was calculated as total saliva volume (ml) divided by the collection time (min) while pH was determined using a digital pH meter.