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Salmon pituitary gonadotropin purified by Sephadex G-100 was effective for spermatogenesis as well as spermiation in hypophysectomized male goldfish ( Carassius auratus ). The same gonadotropin was also effective for vitellogenesis and ovulation in hypophysectomized female goldfish. The hormonal requirement for vitellogenesis (9 injections of 0.5 mg partially purified salmon gonadotropin per 10 g body weight) and for ovulation (1 injection of 0.3 mg per 10g body weight) was greater than that for spermatogenesis (9 injections of 0.1 mg per lOg body weight) and for spermiation (0.03 ing per 1Og body weight). The possibility that there is one functional gonadotropin in the fish pituitary gland which controls the whole maturation phenomenon is discussed.

Response of the regressed testes and seminal vesicles was studied after 30-day treatment with partially purified salmon gonadotropin (SG), ovine luteinizing hormone (LH), and testosterone in 237-day hypophysectomized catfish. Daily treatment with SG (0.1, 1, 10, and 100 μg) and LH (1, 10, and 50 μg) produced a dose-dependent response in the testes and seminal vesicles. A dose of 1 μg of SG reinitiated spermatogenesis, whereas a dose of 100 μg of SG not only fully restored spermatogenesis but also induced spermiation. Treatment with 10 μg of LH produced a spermatogenic response in the testes and secretory activity in the seminal vesicles comparable to those induced by 1 μg of SG. A dose of 50 μg of SG and 100 μg of testosterone were equipotent in inducing spermatogenesis in the testes and secretory activity in the seminal vesicles. LH and testosterone at the dose levels used did not induce spermiation. The possibility of one functional gonadotropin regulating the whole maturation phenomenon in the male catfish is discussed.

After reviewing data on comparative biochemical and biological properties of gonadotropins (GTH) from lower vertebrates, we discuss two main problems: the number of GTHs in each lower vertebrate, and the specificity and evolution of GTHs. It is concluded that: (1) The existence of a single GTH in the teleost, and possibly also in the amphibian and reptile, is the most probable hypothesis. (2) While all GTHs (and TSHs) are probably homologous proteins, an important zoological specificity of GTH does exist. Finally, preliminary results suggest that the gonadal receptors for GTH in lower vertebrates are, as in mammals, associated with an adenyl cyclase activity. The evolution of these “analogous” receptors should be considered together with that of the gonadotropins. It is suggested that the differentiation of the two classes of receptors (respectively, in gametogenetic and steroid-producing tissues) allowed a precise pituitary regulation of the gonads before the appearance of a second pituitary gonadotropin.

Vitellogenin production was induced in immature diploid and triploid coho salmon by the weekly injection of 17 beta-estradiol at 1 mg/kg body wt. There was no significant difference between diploids and triploids for any of the results obtained, i.e., change in plasma vitellogenin and gonadotropin levels, hepatosomatic index, or pituitary gonadotropin content. Plasma vitellogenin levels were significantly higher in 17 beta-estradiol-treated fish than in sham-injected fish within a week of the first injection, and continued to rise with each subsequent injection. Plasma gonadotropin levels, on the other hand, were slightly (but significantly) depressed. The 17 beta-estradiol-treated fish had higher hepatosomatic indices and pituitary gonadotropin contents than sham-injected fish by 3 weeks after the first treatment. These data suggest that the occasional postmeiotic oocytes observed in triploids do not grow to full maturity due, in part, to an absent or diminished estrogen stimulus from the ovary on hepatic vitellogenin production.