Effects of clonidine on basal and cold-stimulated TSH secretion.

Clonidine, injected i.p. 20 min before cold exposure, is able to counteract the blockade induced by alpha-methyl-p-tyrosine of cold-stimulated release of TSH in rats. Under basal conditions the alpha-adrenoceptor stimulating agent, administered into the lateral cerebral ventricle (10 microgram), produces, at 30 min, a sharp increase in plasma TSH that returns to control levels at 60 min. When the drug is given intraperitoneally (0.4 mg/kg) it causes a significant decrease in plasma TSH 120 min after the treatment.