Secretory responses to autonomic stimulation of rat salivary glands following reserpine treatment

Changes in rat parotid saliva protein composition following chronic reserpine treatment and their relation to inanition

Chronic administration of the catecholamine-depleting agent, reserpine (0.5 mg/kg), resulted in a reduction in food intake after 3 days. To differentiate effects of the drug from those of reduced food intake a pair-fed group, whose daily caloric intake was restricted to the amount consumed by the reserpine-treated rats, was included. After 7 days, both the reserpine-treated and pair-fed control exhibited a marked reduction in the volume of saliva collected in a 30 min interval following a secretory stimulus compared to untreated ad libitum-fed controls, and the proportion of salivary proteins attributable to acidic and basic proline-rich proteins and to minor 1b protein were decreased whereas deoxyribonuclease was increased. For two of the salivary proteins (fractions I and V) changes for the reserpine-treated and pair-fed groups were different. Fraction I was reduced in both groups, but exhibited a greater decrease in the pair-fed than in the reserpine-treated, whereas fraction V was significantly increased only in the pair-fed group. Thus many of the salivary changes associated with reserpine treatment may have resulted from the change in feeding habits and not from reserpine treatment per se. The study demonstrates the importance of controlling for food intake under experimental circumstances which may lead to a marked change in daily feeding habits.

Interaction between amphetamine and alpha 2-postsynaptic adrenoreceptors in the rat submaxillary gland

1 The interaction between amphetamine and the alpha 2-adrenoreceptor agonists, clonidine and guanabenz, was studied in the submaxillary gland of anaesthetised rats. 2 Low doses of clonidine (10 micrograms/kg) and guanabenz (10 micrograms/kg) inhibited the secretory responses induced by methacholine and substance P, respectively. 3 Amphetamine (300 micrograms/kg) antagonized the inhibitory effects of both alpha 2-agonists. This dose of amphetamine alone did not show sialagogic effects. 4 Atropine (1 micrograms/kg) diminished the secretory responses to methacholine as much as clonidine (10 micrograms/kg). Amphetamine did not modify the blockade by atropine. 5 Guanabenz (10 micrograms/kg) markedly decreased the secretory responses to substance P, an effect that was also prevented by amphetamine. 6 Reserpine pretreatment (5 mg/kg, i.p., 18 h) did not alter the effect of amphetamine. 7 These results indicate that the interaction between amphetamine and alpha 2-adrenoreceptor agonists is unrelated to the indirect effect of this amine and suggest a direct interaction between the drug and postsynaptic inhibitory alpha 2-adrenoreceptors.

Ca-ATPase activity in salivary glands of rats treated with reserpine, isoproterenol, terbutaline or dobutamine

Ca-ATPase activity (mol Pi/mg protein per min) of submandibular and parotid glands after injection of single or multiple (over seven days) 0.5 mg/kg doses of reserpine was the same as in untreated glands. Twice daily doses (50 mg/kg body wt) of the non-selective beta-adrenergic agonist, isoproterenol, for six days, increased Ca-ATPase specific activity of parotid gland by 17 per cent but that of submandibular gland was the same as controls; with dobutamine, the same dosage caused a 53 per cent decrease in submandibular activity and a 31 per cent decrease in parotid. The activity of the entire parotid gland was markedly increased by all three beta-agonists, and this was generally a reflection of the induced increase in gland size. The submandibular gland had an increase in total Ca-ATPase activity only with isoproterenol. As gland weight did not change after reserpine, total glandular Ca-ATPase activity was also not altered by it. Thus, calcium accumulation and reduction in Ca-ATPase activity are not necessarily related. However, the dobutamine-induced decrease in Ca-ATPase activity of both glands suggests that there is a beta 1-mediated regulation of this enzyme.

The effects of diabetes and autonomic neuropathy on parotid salivary flow in man

Stimulated parotid salivary flow studies were performed on 20 non-diabetic subjects and on 30 patients with insulin-dependent diabetes mellitus who had been screened for autonomic neuropathy using tests of cardiovascular reflexes. Electrical gustometry was performed to detect the taste threshold. The stimulated parotid salivary flow rates of diabetics with no autonomic neuropathy or early parasympathetic autonomic dysfunction alone were similar to those of non-diabetic subjects. Diabetic patients with established parasympathetic autonomic neuropathy had significantly higher salivary flow rates as did those with combined sympathetic and parasympathetic neuropathies. Taste thresholds did not correlate either with the duration of the diabetes or with the presence of autonomic neuropathy. The cause of the increased salivary flow associated with diabetic autonomic neuropathy is unclear. It may represent the removal of a neural inhibitory mechanism which modulates salivary flow, or the effects of long-standing diabetes on salivary secretion.