Inhibition of prolactin secretion by ergot alkaloids.

The effect of various ergot alkaloids on prolactin (Pr) secretion in adult female rats was determined by radioimmunoassay. Ergocorine (ECO) and ergocristine (ECR) in doses of 0.25 to 1.0 mg lowered serum Pr markedly by 1 h with the effect persisting for 24 h at the larger doses. Several other ergots had similar effects while the dihydro derivatives had diverse responses. The pro-oestrous surge of Pr could be blocked by ECR or ECO without interfering with the oestrous cycle. ECO or ECR could suppress the rise in serum Pr induced by oestradiol benzoate (OeB) (5-50 mug) in oophorectomized rats. Perphenazine (PE) stimulation of Pr could be partially antagonized by ECO depending on dose and timing of injections. ECO 2 mg produced an abrupt cessation of lactation with concomitant fall in serum Pr, and ovine prolactin restored this function. Evaluation of pituitary Pr concentration in lactating and intact rats receiving ECO leads to the conclusion that release of Pr from the pituitary is affected. ECO 1 or 2 mg produced a regression of dimethyl-benz(a)anthracene (DMBA) induced rat mammary tumours which could not be reversed by OeB 5 mug, with persisting low serum Pr. PE 1 mg was able to raise serum Pr and stimulated tumour growth. Several of the ergot alkaloids have a profound inhibiting effect on Pr secretion and may be used for studies on Pr action, as well as in medical therapeutics.