β-Adrenergic and Muscarinic Receptors of Parotid Gland following Maintenance of Rats on Liquid Diet

Abstract

Parotid gland of adult rats maintained exclusively on liquid (milk) diet for 7 or 13 days showed a 25% reduction in number of †-adrenoceptors, and after 21 days, the reduction was 33%; with maintenance of rats on Metrecal for 7 days, the decrease was 24% for female rats and 22% for male rats. The decrease in number of muscarinic receptors after 7 or 13 days on milk was 32%, and 38% after 21 days; the decreases for rats on Metrecal for 7 days were 32% for females and 35% for males. In rats maintained on liquid (milk) diet for 7 days, and then denervated by unilateral removal of the parasympathetic and sympathetic innervations to parotid there were decreases of 39–42% in number of β-receptors and 50–52% in muscarinic receptors at 6 or 14 days after denervation (maintenance on liquid diet for 13 and 21 days, respectively) from those of innervated glands of chow-fed rats; denervated glands of rats on chow diet showed the same reduction. Thus, it was concluded that absence of neurally mediated glandular activity, imposed by either diet or surgical removal of the nerves, caused marked decreases in number of both β-adrenergic and muscarinic receptors, but that the presence of the nerves, even though inactive (liquid diet), provided a trophic influence that prevented the more marked decreases seen in the absence (surgical removal) of the nerves.