Assessment of the primary adrenal cortical and pancreatic hormone basal levels in relation to plasma glucose and age in the unstressed Ames dwarf mouse

Abstract

Peripheral glucose concentrations in mammals are maintained within very narrow limits to provide a continuous, uninterrupted supply of this nutrient to tissues. Numerous factors have been shown to influence and/or regulate glucose levels. One such influence is growth hormone (GH) produced by the pituitary somatotrophs. Several animal models of hyposomatotropism are available in which GH secretion or actions are suppressed due to genetic abnormalities. One such model, the Ames dwarf mouse (df/df), has arisen from an autosomal recessive mutation in which GH-, prolactin- (PRL), and thyroid-stimulating hormone (TSH)-producing cell types of the anterior pituitary fail to develop. The current investigation examined the effects of GH deficiency on glucose, insulin, and corticosterone levels using male and female df/df mice and their normal (Df/-) littermates. Additionally, old and young females of both genotypes were used to determine whether aging and GH deficiency interact to influence insulin, corticosterone or glucose levels in these animals. Plasma samples collected from unstressed animals (normal, df/df; young [5 months], old [17-19 months]; male, female) were used. Glucose levels were lower (P < 0.05) in df/df than in Df/- mice regardless of sex and age. A sex difference in Df/- animals was evident--young and old females had significantly lower levels of glucose when compared with young Df/- males. Plasma insulin was elevated (P < 0.05) in old df/df females compared with young df/df and Df/- females. Young Df/- males had the highest insulin levels compared with all genotype and age groups. This observation paralleled results from glucose measurements. Corticosterone levels were highest in young Df/- females and lowest in young Df/- males, with df/df animals falling between these values. Plasma corticosterone levels in old Df/- females did not differ from the values measured in dwarfs. The present findings indicate that glucose and factors affecting glucose levels are altered in the df/df mouse. These results provide new insights into the roles GH may play in glucose metabolism and perhaps also in adiposity which is a common characteristic of Df/- aged females from this line of mice.