Oxytocin influences preovulatory follicular development and advances ovulation in rats

Abstract

Oxytocin has been shown to advance gonadotropin secretion in pro-estrus rats. The effects that oxytocin-induced changes have on the ovary were investigated in this study. Oxytocin administered to rats at proestrus 09.00 h, 10.00 h and 11.00 h advanced follicular growth, progesterone secretion, and the time of ovulation. However, both treated and control groups of rats ovulated similar numbers of oocytes and the oocytes released were of similar fertility. Because oxytocin has been shown to induce early LH and FSH release the effects of oxytocin administration on the ovary were possibly an indirect action involving the pituitary. The results of this investigation indicate that exogenous oxytocin alters, the timing but not the fertility of periovulatory events.Oxytocin has been shown to influence follicular de¬ velopment and ovulation in cyclic mice (1). Al¬ though the hormonal factors mediating this effect were not determined, it has since been demon¬ strated that oxytocin administered to rats on the morning of pro-estrus could advance the LH surge (2). A vital role for oxytocin at pro-estrus was in¬ dicated by abolishing the in vivo LH surge with oxytocin receptor antagonists (2,3). A direct gonadotropin-releasing activity of oxytocin on rat pitu¬ itary cells in vitro, acting via specific receptors has been established (4). Whether gonadotropins released by oxytocin treatment of pro-estrus rats have normal physio¬ logical activity was not demonstrated. Therefore the current study was designed to determine if oxy¬ tocin treatment altered follicular growth and ovu¬ lation, and the ability of ovulated oocytes to be fer¬ tilized in vivo. Material and Methods AnimalsFemale Wistar rats were obtained at 12 weeks of age.They were housed 5 animals to a cage under controlled humidity, temperature (22°C) and lighting (lights on be¬ tween 05.00 and 19.00 h). Rats were provided with pel¬ leted food and fresh water ad libitum. Vaginal smears were taken each morning to monitor estrous cycles. Only those rats exhibiting three or more consecutive four-day cycles were used.Effect of oxytocin on follicular development and ovulation Experimental rats received injections of oxytocin (Syntocinon®, Sandoz, Switzerland) (10 mlU/g ip) at pro-estrus : 09.00 h, pro-estrus: 10.00 h, and pro-estrus: 11.00 h (2) in a volume of 0.25 ml. Control animals received equiv¬ alent injections of saline. At 3-h intervals between proestrus: 12.00 h and estrous: 06.00 h groups of 5 rats were bled and killed by cardiac punction under pentobarbitone anesthesia. Ovulation rates (ova ovulated per rat) were determined by the retrieval of ova from the oviducts. The ovaries were removed for histological processing. For the measurement of plasma progesterone, blood was col¬ lected from the tail vein of additional rats under light halothane anesthesia. Effect of oxytocin on oocyte fertilization in vivoThe ability of oocytes ovulated after oxytocin treatment to be fertilized and develop into normal litters was investi¬ gated. Pro-estrus rats were mated after receiv...

Effect of oxytocin infusion on secretion of progesterone and luteinizing hormone and the concentration of uterine oxytocin receptors during the periovulatory period in cloprostenol-treated ewes

“…Early work on the rabbit found that treatment with oxytocin or oxytocin antiserum shortly before mating or hCG treatment blocked ovulation (Brinkley & Nalbandov, 1963;Roca et ., 1978). Robinson et al (1985) found that administration of oxytocin to cyclic mice in early pro-oestrus induced more preantral follicles and an earlier ovulation than in control mice, and similar exper¬ iments in rats advanced the time of ovulation by about 3 h (Robinson & Evans, 1991). However, all oxytocin-treated ewes in the present experiment ovulated, and the histological appearance of the corpus luteum approximately one day after ovulation did not differ following treatment.…”

Alterations in gonadotropin, apoptotic and metabolic pathways in granulosa cells warrant superior fertility of the Dummerstorf high fertility mouse line 1

“…Female mice lacking OXT are fertile and able to deliver pups [ 35 ]. Administration of OXT has no effects on the number of follicles and the ovulation rate [ 36 , 37 ], but the abundance of Oxtr mRNA in GCs suggests a role of OXT in follicular development. OXT has been shown to stimulate the production of LH in the pituitary [ 38 ].…”

The effect of oxytocin on the time of ovulation, conception, and embryonic survival in swine

“…(Wathes et al 1992). rather than with direct effects on the process of or.ulation as observed in the rat (Evans et al 1989;Robinson and Evans 1991). It is possible that the quantify of OT was not sufficient to elicit the expected response.…”