5-Hydroxytryptamine causes contraction of smooth muscle cells in preovulatory hamster follicles.

Abstract

AbstractWe have examined the effect of 5‐hydroxytryptamine (5‐HT) on ovaries removed from hamsters and placed in culture 12 or 13 hours after hCG injection. The four responses to 5‐HT which were studied include: (1) contraction of follicular smooth muscle cells (SMC), (2) formation of a V‐shaped constriction in the base of follicles, (3) changes in the profile of follicles, and (4) changes in intrafollicular pressure. Our results show that 10−3 M 5‐HT alters the ultrastructure of follicular SMC to that characteristic of a contracted state. The contraction of these SMCs produces in turn: (1) a V‐shaped constriction in the base of the follicle similar to that observed in unstimulated 13 hour ovaries undergoing in vitro ovulation (Martin and Talbot, '81a), and (2) a change in the profile of the follicle which becomes taller and more spherical, but not identical to the “true” tall follicle seen during normal in vitro ovulation. The fact that 5‐HT does not change the follicle to a “true” tall profile and does not induce immediate ovulation in most cases (even though SMC are contracted) suggests to us that the apices of these follicles were not sufficiently weakened by enzymes to permit immediate rupture when SMC contracted. The response of SMC to 5‐HT was immediate, rapid, sustained at least 10 minutes, and could be inhibited by methysergide. The latter observation suggests that 5‐HT interacts with “D” receptors of SMC and not “M” receptors of nervous tissue. The degree of contraction elicited by 5‐HT varied from one follicle to another; many SMC did not appear maximally contracted by morphological criteria. Intrafollicular pressure increased in most follicles treated with 5‐HT; pressure returned to initial levels relatively quickly, presumably because fluid was able to seep through developing ruptures in the apex. Intrafollicular pressure does not increase during unstimulated in vitro ovulation (Schroeder and Talbot '82). We interpret the intrafollicular pressure data of this study to mean that 5‐HT elicits a much more rapid contraction of SMC than would ordinarily occur in vitro. Thus, SMC contraction in follicles not stimulated by 5‐HT would be a slow, gradual, process allowing constant or decreasing levels of pressure to be maintained. Our observations are important in directly showing that: (1) 5‐HT stimulates contraction of SMCs in hamster follicles, and (2) this contraction produces a V‐shaped constriction in the base of the follicle and a change in the profile of the follicle, and (3) that intrafollicular pressure will increase abruptly upon strong, simultaneous contraction of follicular SMC. These observations provide further support for our earlier statement that SMC function in hamster ovulation (Martin and Talbot,'81a).