Effect of oxytocin, IBMX and dbcAMP on rabbit ovarian follicles

Oxytocin (OT) and protein kinase A (PKA), a possible intracellular mediator of hormone action in the ovary, can be potent activators of ovarian functions and fertility. Nevertheless, action of OT on ovarian follicle atresia has not been studied yet. Only single administration of PKA activators [3-isobutyl-1-methyl-xanthine (IBMX) and dibutyryl cyclic adenosine monophosphate (dbcAMP)] on ovarian follicle atresia was studied previously. The aim of this study was to examine the effect of OT (single treatment per one reproductive cycle, multiple treatments for three cycles), IBMX and dbcAMP (multiple treatments) on folliculogenesis and follicular atresia in rabbit. The ovarian cycle in control females was induced only by gonadotropins. Experimental females received co-administration of gonadotropins with OT, IBMX or dbcAMP (at 50 μg/female). All females were artificially inseminated. Single-treated females were euthanized after 18-19 h. Multiple-treated females were euthanized after the third reproductive cycle. Histological sections of the ovaries were prepared and evaluated by a light microscopy. The follicles were divided into four classes according to the structure of granulosa and theca cells as follows: none or small atresia, cystic atresia, obliterative atresia and atresia associated with luteinization. The ovaries from the control and experimental females, treated during one reproductive cycle or three cycles, were compared. Single OT co-administration increased proportion of follicles with atresia associated with luteinization, but not other types of atresia. No influence of multiple OT co-administration on follicular atresia was recorded. Multiple IBMX and dbcAMP co-administration decreased the proportion of atretic follicles and increased the proportion of healthy follicles without atresia.