Concurrent pulsatile secretion of luteinizing hormone and follicle-stimulating hormone during different phases of the estrous cycle and anestrus in beagle bitches

The 6-h secretory profiles of LH and FSH and the possible concordance betwe en the episodic release of LH and FSH were studied in 6 beagle bitches duri ng early, mid-, and late anestrus and during the follicular and luteal phas es of the estrous cycle. Plasma samples were obtained at 10-min intervals v ia jugular venipuncture. In all stages of anestrus and in the luteal phase, FSH and LH secretion was pulsatile. All FSH pulses coincided with LH pulse s. 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 concentratio n was low compared with the maximum peak levels, whereas FSH pulses were ch aracterized by relatively low peaks compared with the basal levels. In cont rast to the basal plasma LH levels and the area under the curve (AUC) for L H, 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 thi s 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 f requency of LH pulses, a shorter duration of the LH peaks, and a tendency t o 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 r eleased in concordance and that progression from early to late anestrus is associated with an increase in basal plasma FSH concentration without a con comitant rise in basal plasma LH concentrations. The latter suggests that i n the bitch an increase in circulating FSH should be considered to be a cri tical event required for the initiation of ovarian folliculogenesis and con sequently for the termination of anestrus.