EFFECT OF l-DOPA ON MILK EJECTION AND PROLACTIN RELEASE IN LACTATING RATS

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Abstract
SUMMARY: The effect of l-DOPA on milk ejection and on prolactin release during 30 min of suckling was studied in lactating rats. Various doses of l-DOPA (1·25, 2·5, 5 and 10 mg/100 g body wt) were injected i.p. 30 min before the suckling period. Control rats were injected with 0·9% NaCl solution only. An inhibition of milk ejection proportional to the dose of drug administered was obtained. The dose of 10 mg completely blocked milk ejection but 1·25 mg had no effect. A normal milk-ejection response was obtained with a small dose of oxytocin injected immediately before nursing into mothers treated with 10 mg l-DOPA, indicating that the blocking effect was not due to a lack of mammary gland response. In control mothers, serum prolactin levels increased from 67·2 ± 25·9 (s.e.m.) to 950·3 ± 118·7 ng/ml after a 30 min suckling period. l-DOPA (5 and 10 mg) prevented the release of prolactin induced by suckling, but 1·25 and 2·5 mg l-DOPA had no effect. The results indicate that oxytocin and prolactin release induced by suckling in lactating rats is inhibited by an increase of catecholamines at the hypothalamic-hypophysial axis.

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