ScienceAsia 21 (1995): 243-252 |doi: 10.2306/scienceasia1513-1874.1995.21.243

EVIDENCE FOR MORPHINE-INDUCED PRL RELEASE IN CYNOMOLGUS MONKEYS (Macaca fascicularis)

SUCHINDA MALAIVIJITNOND^a AND PUTTIPONGSE VARAVUDHI^b

ABSTRACT: The effect of morphine hydrochloride, u-opiate receptor agonist, at doses of 0, 0.2, 0.4, 0.8 and 1.6 mg/kg on serum PRL leveis was investigated in adult female, pubertal and adult male cynomolgus monkeys. Nearly all monkeys showed a prompt rise of serum PRL levels as early as 15 min after subcutaneous morphine injection and reached a maximum value within 30-60 min. Morphine significantly increased serum PRL levels in a dose-dependent manner in which it started from dose 0.2 mg/kg. Except for the highest dose treatment (1,6 mg/kg morphine), serum PRL levels were gradually decreased to the basal levels at 6 1/2 h (390 min). In the same dose, morphine produced a higher and longer increment of PRL levels in female monkeys than pubertal and adult male monkeys, respectively. Indeed, serum PRL levels were never exceeded 1,000 mIU/L at any time points of the study onset in all doses treatment in adult male monkeys. These results have provided evidence supporting an involvement of endogenous opiates in the regulation of PRL release and suggested the possibility of difference in sex and age of lactotroph population in the adenohypophysis of these monkeys.

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a Department of Biology, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand.
b Emeritus Professor, Primate Research Unit, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand.

Received May 15, 1995