GENERAL AND COMPARATIVE ENDOCRINOLOGY 31, 435-441 (1977) Plasma Testosterone Levels in Male Turtles, Chrysemys picta, following Single Injections of Mammalian, Avian and Teleostean Gonadotropinsl V. LANCE, C. SCANES,* AND IAN P. CALLARD~ Depurtment of Biology, Boston University, Boston, Massachusetts 02215; and *Department of Animal Physiology. Unirzersity of Leeds, Leeds, Yorks. U.K. Accepted December 2, 1976 The response of male turtles (Chrysemys picta) to single injections of either mammalian (human, ovine), avian (domestic hen) or teleostean (salmon) gonadotropins was studied at different points of the testicular cycle (May, July, November) by measurement of plasma testosterone. Mammalian FSH’s and avian FSH and LH were markedly stimulatory, and the responses were qualitatively and quantitatively similar. Further, the condition of the testis at the time of injection did not appear to affect the response, with the exception that it was quantitatively less in May. The response was characterized by: (a) Rapidity, reach- ing maximum or near maximum between 1 and 2 hr postinjection. (b) Magnitude, rising from 10 to 20 ng T/100 ml plasma to 1200 ng/lOO ml plasma. (c) Duration, not returning to original plasma levels of T until between 96 and 192 hr postinjection. Injections of purified ovine and human FSH at levels calculated to be equivalent in hormone content to 50 pg of ovine FSH standard duplicated the response. The response was dose related, a 50 pg dose of ovine FSH evoking a response about IO-fold that of a 5 pg injection. Injections of up to 50 pg of NIH ovine LH standard, or 25 pg purified ovine LH only doubled plasma T levels and 100 pg of teleostean gonadotropin had no effect. In a previous study (Callard et al., 1976) we demonstrated a marked stimulatory ef- fect of ovine FSH on plasma testosterone in the male turtle at three different times of the year, in the presence and absence of the pituitary gland. In these experiments ovine LH had no effect. In order to obtain a more precise idea of the possible site of action of the gonadotropin (interstitial or tubular) it was judged important to rule out long-term morphogenetic effects of the hormones on the testicular elements. Thus, study of hormone action in the time immediately fol- lowing a single injection might be expected to reflect the action of the hormone on the functional cellular elements present in the testis at the time of single injections. In the ’ Supported by NSF-BMS-75-18910 to IPC. ’ Please address reprint requests to IPC at Boston University. current study, we have examined the ef- fects of various gonadotropins adminis- tered in spring, summer and fall. This is necessary since Leydig cells are hyper- trophic in spring and atrophic in summer and early fall; spermatogenesis begins in early summer and continues into the fall (Callard et al., 1976). MATERIALS AND METHODS Animuls. Male Chrysemys picta obtained from Wisconsin in summer, were maintained outside under natural lighting conditions in 6 ft diameter pools con- taining rocks to allow basking. The turtles were thus able to select preferred body temperature. The ani- mals were fed ground, raw fish ad lib. once weekly. Animals obtained in November were maintained in- doors t25ianimalsipool) on a 16 hr photoperiod with heat lamps for basking. Experimental protocol. After weighing and iden- tification of the turtles, a hole was drilled through the plastron to expose the great vessels leading from the heart. Hormones were administered in 0.5 ml 0.65%) 435 Copyright @ 1977 by Academic Press. Inc. All rights of reproduction in any form reserved. ISSN 0016.6480