Effects of thyroid function on submaxillary gland sensitivity to autonomic nervous drugs

The effect of changes in thyroid function on the action of autonomic drugs upon the secretion of saliva by the submaxillary glands was studied in male Wistar rats. Hyperthyroidism was induced by the sc administration every 12 h of 10 micrograms/100 g bw of L-triiodothyronine; hypothyroidism was induced by surgical thyroidectomy 2 weeks before the experiments. The dose-response curves to increasing doses of isoprenaline, norepinephrine or methacholine showed in hyperthyroid animals increased salivary secretion, while in hypothyroid animals the dose-response to the drug was reduced. The threshold dose for isoprenaline was reduced in hyperthyroid animals and increased in hypothyroid ones. The threshold dose for norepinephrine did not change in hyperthyroid or hypothyroid animals while that for metacholine was decreased in hyperthyroid ones. When norepinephrine was given to alpha-blocked animals (with phentolamine) the difference in the dose-response curves between hyperthyroid and control animals was increased. But when norepinephrine was given to beta-blocked animals (with propranolol) the difference between the dose-response curves of hyperthyroid and control animals disappeared. The results above presented show that the sensitivity of the submaxillary salivary glands of rats to some adrenergic and cholinergic drugs was altered by the thyroid hormone. The effect was greater in the responses mediated by beta receptors. The structural changes in these glands may have some role in these effects.