Role of LH pulse amplitude in controlling rat ovarian oestradiol-17  secretion in vitro

Abstract

Ovaries from di-oestrous rats were removed and placed in perifusion culture: 4-6 ovaries were cultured for 3 h with (1) no gonadotrophin; (2) tonic FSH (200 ng/ml); (3) tonic LH (30 ng/ml); (4) tonic FSH and tonic LH; (5) tonic FSH and hourly pulses of 40 ng LH/ml; or (6) tonic FSH and hourly pulses of 50 ng LH/ml. The total amount of LH administered was 3060 ng LH, regardless of mode of delivery. Perifusate was collected every 10 min and assayed for oestradiol-17 beta by RIA. The total amount of oestradiol-17 beta secreted was not altered by any treatment except when LH was administered in hourly pulses with an amplitude of 50 ng/ml; the total amount of oestradiol-17 beta secreted in 3 h was increased by 300% (P less than 0.05). Without gonadotrophic stimulation, oestradiol-17 beta was secreted at a constant rate (4.48 +/- 0.21 pg/mg 10 min-1). Tonic gonadotrophin stimulation did not alter this pattern. However, pulses of 50 ng LH/ml but not 40 ng LH/ml resulted in periodic increases in oestradiol-17 beta secretory rates. Thus, oestradiol-17 beta secretion is stimulated by LH pulses with the degree of stimulation dependent, in part, on the amplitude and/or the rate of change of the LH pulse.

Differential Effects of Pulsatile Versus Continuous Follicle-Stimulating Hormone Delivery on the Production of Cyclic Adenosine 5′-Monophosphates and the Accumulation of Cytochrome P450 Cholesterol Side-Chain Cleavage Enzyme mRNA in Perifused Porcine Granulosa Cells1

“…Less frequent pulsatile administration of FSH at either concentration did not enhance SCC mRNA accumulation above basal. Our inferences regarding this molecular endpoint of FSH action are in agreement with previous functional studies that demonstrated that pulses of gonadotropins are more efficacious than continuous hormone exposure in increasing ovarian steroid production, follicular development, and luteinization [26][27][28][29][30]35]. The fractional increases in SCC mRNA accumulation observed here under perifusion conditions are consistent with the magnitude of the increases reported during static culture of porcine granulosa cells [36].…”

“…More direct assessments of the role of pulsatile gonadotropin secretion on ovarian function have utilized perifusion systems. Peluso et al [26,27] observed that whole rat follicles secreted increased amounts of estradiol and had an increased proportion of mid-sized growing follicles when exposed to pulsatile versus tonic FSH stimuli. Furthermore, Peluso and Steger suggested that the effect of LH pulses given in the presence of a constant infusion of FSH depended on a threshold concentration of LH, as well as the rate of increase in LH concentrations [28].…”

Theca: the forgotten cell of the ovarian follicle

“…LH is released in a pulsatile manner, and the frequency and amplitude of these pulses vary across the reproductive cycle in response to ovarian steroidogenic feedback. The pulse frequency of LH dictates the amounts of steroid hormones produced, where each pulse of LH is followed by an increase in androstenedione and estradiol secreted from the ovary in many species (Baird et al 1976, 1981, Peluso et al 1984. When theca cells were cultured in vitro, low levels of LH also stimulated androgen production (Campbell et al 1998, Ryan et al 2008, whereas, at high doses, LH inhibited androstenedione production and stimulated progesterone secretion as well as changing cell morphology indicating that the high LH levels induced luteinization in these cells (Campbell et al 1998).…”

The effect of monosaccharide sugars and pyruvate on the differentiation and metabolism of sheep granulosa cells in vitro

“…Much of the current research suggests an indirect effect of glucose on ovarian function via nutritionally induced metabolic hormones such as insulin, insulin-like growth factor 1 (IGF1) and leptin (Peluso et al 1984, Davis et al 1990, Munoz-Gutierrez et al 2002. Conversely, glucose may also act directly on the ovary.…”