Granulosa cell responsiveness (in vitro) at two stages of differentiation in cows and one stage of differentiation during puberal transition in heifers

Abstract

Differentiation of granulosa cells (GC) into luteal cells and mechanisms subserving attainment of puberty are two areas of interest in reproductive endocrinology of the bovine. The first study described herein compared GC responsiveness at early (1 to 2 h) and late (14 to 16 h) stages of differentiation following the onset of estrus (and presumably the luteinizing hormone surge) in cows. Granulosa cells that were collected at the early stage of differentiation had a higher in vitro response (progesterone production) to luteinizing hormone, forskolin (adenylate cyclase stimulator) and diacylglycerol (phospholipid intermediate and protein kinase-C stimulator) than GC that were collected at the late stage of differentiation. Highly differentiated GC, however, produced more progesterone following culture with prostaglandin-E2 than less differentiated GC. In summary: 1) GC differentiation encompasses a refractory period to in vitro stimulation, which possibly involves both receptor and adenylate cyclase function, 2) GC differentiation may involve acquisition of responsiveness to prostaglandin-E2, 3) phospholipid metabolism may be involved with GC differentiation. The second study compared GC responsiveness during puberal transition at a late stage of differentiation (14 to 16 h following the onset of estrus) in heifers. Granulosa cells were collected following first estrus (FE: preceeded by low progesterone; < 1 ng/ml) or following subsequent estrus (SE: preceded by high progesterone; > 1 ng / ml). Luteinizing hormone ± cholesterol and forskolin in the absence of cholesterol stimulated GC progesterone production to a greater degree following FE than SE. In summary: 1) GC collected following SE were refractory to in vitro stimulation when compared with GC collected following FE, 2) whether the refractory state in GC collected following SE was due to a more competent LH surge and a more highly differentiated cell type remains to be determined. Comprehension of the controlling endocrine parameters for processes involved with GC differentiation may provide a basis for the identification of mechanisms responsible for enhanced or suppressed fertility in cows and heifers.