Concurrent Pulsatile Secretion of Luteinizing Hormone and Follicle-Stimulating Hormone during Different Phases of the Estrous Cycle and Anestrus in Beagle Bitches

Abstract

The 6-h secretory profiles of LH and FSH and the possible concordance between the episodic release of LH and FSH were studied in 6 beagle bitches during early, mid-, and late anestrus and during the follicular and luteal phases of the estrous cycle. Plasma samples were obtained at 10-min intervals via jugular venipuncture. In all stages of anestrus and in the luteal phase, FSH and LH secretion was pulsatile. All FSH pulses coincided with LH pulses. However, the mean duration of the FSH pulse (115 min) was significantly longer than that of the LH pulse (72 min). The basal plasma LH concentration was low compared with the maximum peak levels, whereas FSH pulses were characterized by relatively low peaks compared with the basal levels. In contrast to the basal plasma LH levels and the area under the curve (AUC) for LH, the basal plasma FSH levels and the AUC for FSH increased significantly as anestrus progressed. During the follicular phase, the secretory pattern of LH was characterized by frequent increases of short duration. During this phase, the basal plasma FSH concentration was relatively low, whereas the basal plasma LH level was high in comparison with that in the other phases of the estrous cycle. The luteal phase was characterized by an increased frequency of LH pulses, a shorter duration of the LH peaks, and a tendency to a lower amplitude of both LH and FSH peaks compared with values observed during anestrus. It is concluded that in the bitch, FSH and LH pulses are released in concordance and that progression from early to late anestrus is associated with an increase in basal plasma FSH concentration without a concomitant rise in basal plasma LH concentrations. The latter suggests that in the bitch an increase in circulating FSH should be considered to be a critical event required for the initiation of ovarian folliculogenesis and consequently for the termination of anestrus.

Basal and GnRH-induced secretion of FSH and LH in anestrous versus ovariectomized bitches

“…In agreement with the findings of others, GnRH administration elicited a distinct release of LH [4,[7][8][9][10] and FSH [10]. The course of the GnRH-induced surges in FSH and LH in the anestrous bitches was comparable to what has been reported previously for spontaneous FSH and LH pulses in anestrous bitches [1]. The GnRH-induced plasma LH increments above the pre-GnRH levels were much greater than the corresponding FSH increments.…”

“…Although all pre-GnRH plasma LH concentrations were higher in OVX dogs than in sexually intact dogs, measurement of circulating LH concentration in a single sample has limited potential for distinguishing between OVX and sexually intact bitches. Taking into account the strong pulsatile nature of LH release [1,13], an overlap in the plasma LH concentration between larger groups of intact and OVX bitches may be expected. Indeed, in the current study GnRH-induced LH increments in the intact bitches overlapped pre-GnRH plasma LH concentrations in the OVX bitches.…”

“…The neuroendocrinological mechanisms responsible for the release of follicle stimulating hormone (FSH) and luteinizing hormone (LH) by the pituitary are very complex. It is generally accepted that these gonadotropins are secreted in a pulsatile fashion [1] in response to the similarly pulsatile release of gonadotropin releasing hormone (GnRH). The gonadotropins stimulate ovarian hormone secretion, which in turn regulates www.theriojournal.com Theriogenology 67 (2007) [1039][1040][1041][1042][1043][1044][1045] the gonadotropins via a negative feedback mechanism (long-loop negative feedback).…”

Effects of the dopamine agonist cabergoline on the pulsatile and TRH-induced secretion of prolactin, LH, and testosterone in male beagle dogs

“…In bitches, administration of dopamine agonists during both the luteal phase and anoestrus results in shortening of the interoestrous interval in the bitch [23][24][25][26]. It has been shown that this dopamine agonist-induced shortening of the interoestrous interval in the bitch is associated with an increase in circulating FSH concentration [27].…”

Differential regulation of the secretion of luteinizing hormone and follicle-stimulating hormone around the time of ovulation in the bitch

“…In dogs, follicle stimulating hormone (FSH) pulses appear to occur www.journals.elsevierhealth.com/periodicals/the Theriogenology 66 (2006) [1419][1420][1421][1422] concomitantly with LH pulses in all stages of the estrous cycle and anestrus [3]. The pre-ovulatory LH-surge is also associated with a surge in FSH secretion [4].…”