In vivo steroidogenic effects of homologous pituitary ventral lobe extract in the spiny dogfish, Squalus acanthias.

Pregnant Squalus acanthias were injected intravenously with aqueous extract equivalent to three pituitary ventral lobes (VL). Blood samples were withdrawn by caudal sinus puncture at intervals over a period of 72 hr and plasma progesterone, testosterone, and estradiol-17 beta measured by radioimmunoassay. Early pregnancy animals (Stage A) failed to respond, but mid-pregnancy animals (Stage C) responded to VL with significant increases in plasma steroids. Plasma progesterone and testosterone were increased sevenfold and plasma estradiol-17 beta fourfold by 10-24 hr postinjection. These studies demonstrate pregnancy stage-dependent differences in gonadal sensitivity to a pituitary ventral lobe gonadotropic moiety.