In vitro effects of homologous prolactins on testosterone production by testes of tilapia (Oreochromis mossambicus)

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The tilapia, Oreochromis mossambicus, produces two prolactins designated tPRL177 and tPRL188 to indicate the number of amino acid residues in each. The direct in vitro actions of tPRL177 and tPRL188 on basal and ovine luteinizing hormone (LH)-induced testosterone production in minced testes of courting and noncourting (bachelor) tilapia were examined. Courting males were housed with females and were used as soon as they built a spawning pit; noncourting males were housed with other males and were used when they appeared female-like in coloration. The in vitro culture system consisted of two phases. In phase 1 (0-10 hr), testicular tissue was incubated without (control) or with the tPRLs-both alone and together and in doses ranging from 0.5 to 32 μM. In phase 2 (10-16 hr), the culture medium was replaced with medium containing 6.25 μM (0.25 μg/ml) ovine LH. Testosterone production during both phases was determined by radioimmunoassay of the medium. The tPRLs stimulated testosterone production during phase 1 in courting males (by 25%) but not in noncourting males. Exposure to either or both tPRLs in phase 1 enhanced the response of testicular tissue from courting males to ovine LH (by 10%) and inhibited the response of minced testes taken from noncourting males (by 12%). This is the first evidence to demonstrate direct gonadal activity of homologous PRL in a teleost. © 1992.

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General and Comparative Endocrinology