Effects of insulin, insulin-like growth factor I, and gonadotropins on bovine granulosa cell proliferation, progesterone production, estradiol production, and(or) insulin-like growth factor I production in vitro1

Abstract

The objectives of the present studies were to determine the effect of insulin, insulin-like growth factor I (IGF-I), testosterone, and FSH on proliferation, progesterone production, and(or) estradiol production of bovine granulosa cells. In addition, existence of IGF-I mRNA in granulosa cells and in vitro IGF-I production by granulosa cells were assessed. Cells from small (1 to 5 mm) and large (> or = 8 mm) follicles were collected from cattle and cultured for either 3 or 4 d. When cells from small follicles were cultured, insulin (.1 to 10 micrograms/mL) and IGF-I (100 to 400 ng/mL) increased (P < .05) cell numbers compared with controls. Insulin alone or IGF-I alone increased (P < .05) progesterone production per cell by severalfold on d 4. In cells from both sizes of follicles, insulin (1 microgram/mL), in the presence of FSH, increased estradiol production per cell. In contrast, IGF-I (100 ng/mL) inhibited estradiol production by cells from small follicles and stimulated estradiol production by cells from large follicles. Insulin-like growth factor II (100 ng/mL) and insulin at higher doses (> or = 5 micrograms/mL) had no effect on estradiol production by cells from small and large follicles. Granulosa cells contained four IGF-I mRNA transcripts and produced IGF-I in vitro. These results support the hypothesis that insulin and IGF-I may have direct local effects on bovine ovarian function, and that these effects are influenced by dose and size of follicle.

Milk production, milk composition, and reproductive function of dairy cows fed different fats

“…It has been suggested that improved conception rate could be a result of increased concentrations in plasma cholesterol (Spicer et al 1993), although this hypothesis was not supported by the results of the present experiment. In fact, cows fed FLAX had lower plasma cholesterol concentration and a better conception rate than those fed MEGA.…”

“…Plasma concentrations of total and HDL cholesterol increased from week 9 to week 19 of lactation, but the increase was greater for cows fed MEGA than for those fed FLAX, which resulted in a significant interaction between week and diet. Fat supplementation is known to increase blood cholesterol (Spicer et al 1993;Garcia-Bojalil et al 1998), which would explain the increase observed in the present experiment from week 9 to week 19 as cows began to receive fat from week 9. Moreover, the greater increase in blood cholesterol for cows fed MEGA compared with those fed FLAX corroborate the depressing effect of omega-3 FA as supplied by flax on blood cholesterol already reported in humans (Cunnane 1995).…”

“…According to Spicer et al (1993), insulin is a powerful stimulator of follicular cell development. However, in the present experiment, it is unlikely that insulin was the only factor involved in follicle development as cows fed MEGA and FLAX had similar plasma insulin concentration.…”

Insulin-Like Growth Factor-I as a Possible Hormonal Mediator of Nutritional Regulation of Reproduction in Cattle

“…Cellular localization studies have identified the granulosa cell as the major ovarian cells concerned with IGF-I gene expression and production [68,78]. IGF-I mRNA is also expressed in CL, and its highest expression was observed during the early, mid and late luteal phases [77].…”

Pré-tratamento com somatotropina bovina (rbST) na superovulação de doadoras da raça Holandesa

“…O mecanismo pelo qual o rbST aumentou o percentual de embriões viáveis não é possível de ser explicado neste experimento. O fato do rbST ter elevado as concentrações plasmáticas do hormônio do crescimento (Lucy, 2000), do IGF-I e da insulina (Lucy, 2002), provavelmente se explica pelo efeito desses hormônios sobre maturação dos ovócitos (Pavlok et al, 1996) por efeito direto (Izadyar et al, 1998) ou pela estimulação das células da granulosa (Spicer et al, 1993), além de poderem agir nos estádios iniciais do desenvolvimento embrionário (Kim et al, 1993).…”