Amino acid transport in follicles isolated from the rabbit ovary

The model amino acid alpha-aminoisobutyric acid (AIB) has been used to investigate amino acid transport in follicles isolated from rabbit ovaries. LH markedly increased AIB transport, while incubation with FSH, cAMP or dbcAMP failed to increase the process. Several kinds of inhibitors have been utilized to characterize follicular AIB transport as an energy dependent process and apparently independent of follicular steroidogenesis. The rates of AIB efflux from preloaded follicles were measured in the presence and absence of LH; the rate measurements suggest that only the rate of entry of AIB into follicular cells is stimulated by the gonadotropin. Further experiments used inhibitors of RNA and protein synthesis to examine the relationship between AIB transport and the synthesis of macromolecules. Whereas blocking RNA synthesis suppressed the LH effect on AIB transport, inhibitors of protein synthesis increased the rate of AIB movement into follicles. The in vitro transport of AIB was also studied in follicles isolated 2 hr after mating and in ovulated follicles which were obtained 12 h after coitus. AIB transport rate showed a rise following mating but fell to less than precoital rates in ovulated (12 h) follicles. Transport in both 2 and 12 h follicles proved unresponsive to LH stimulation. Taken together, these studies suggest that AIB transport in isolated ovarian follicles is a LH-sensitive, energy-dependent process. Although AIB transport changes in a pattern qualitatively similar to that previously reported for postcoital protein synthesis, LH stimulation of the two processes may be via different mechanisms.