Insulin-Like Growth Factor-I, Insulin-Like Growth Factor-Binding Proteins, and Gonadotropins in the Hypothalamic-Pituitary Axis and Serum of Nutrient-Restricted Ewes1

Abstract

Body condition scores (BCS) of ovariectomized estradiol-treated ewes were controlled to examine effects of suboptimum BCS on insulin-like growth factor (IGF)-I, IGF-binding proteins (IGFBPs), and LH in the anterior pituitary gland, hypophyseal stalk-median eminence (SME), and circulation. Serum LH increased in ewes with BCS (1 = emaciated, 9 = obese) > 3 (HIGH-BCS), but not in ewes with BCS </= 3 (LOW-BCS), after onset of the breeding season. Concentrations of LH and LHbeta subunits in anterior pituitary glands were lower in LOW-BCS than in HIGH-BCS ewes. Serum IGF-I was lower in LOW-BCS than in HIGH-BCS ewes but did not differ in SME or anterior pituitary glands. In serum, the 44-kDa IGFBP-3 and 24-kDa IGFBP-4 were lower in LOW-BCS than in HIGH-BCS ewes. In anterior pituitary glands, IGFBP-2 tended to be higher in LOW-BCS than in HIGH-BCS ewes. In the SME, IGFBP-2, -3, and -5 were lower in LOW-BCS than in HIGH-BCS ewes. Low body condition may inhibit the increased secretion of LH associated with the onset of the breeding season by altering relative amounts of IGFBPs within the hypothalamic-pituitary axis.

Effects of dietary supplementation and parity of dam on plasma concentrations of Insulin-like growth factor (IGF)-I and IGF-binding protein-3 during post-partum period in dromedary camels

“…In ewes, Snyder et al (1999) found that plasma IGFBP-3 levels were increased in high than in low body condition score groups. In human, plasma IGFBP-3 concentrations are known to be influenced by growth hormone secretion (Cohen and Nissley, 1976), age, pubertal development, nutrition and hepatic function (Blum et al, 1991).…”

Concentraciones de LH en periodos de transición reproductiva en cabras criollas x Nubia con diferente condición nutricional

“…Respecto al efecto del estado nutricional durante los periodos de transición reproductiva, se ha observado que una baja condición corporal en ovejas (25,26,27) , o un periodo prolongado de subalimentación en cabras de baja estacionalidad reproductiva (23) , afectan la secreción de LH. Sin embargo, no existen estudios que hayan descrito una reducción en las concentraciones séricas de esta hormona, debido a restricciones temporales en el consumo de alimento, incluso en cabras con altas reservas corporales de energía.…”

“…About the effect of nutrition during periods of reproductive transition, there has been observed that a low body condition in ewes (25,26,27) , or a prolonged period of under-nourishment in low reproductive seasonality goats (23) , affect LH secretion. However, there are not studies describing a reduction in serum concentrations of this hormone, due to temporary restrictions on the feed intake, even in goats with high body energy reserves.…”

Insulin-Like Growth Factor Binding Proteins in the Bovine Anterior Pituitary

“…Rodent pituitaries secrete IGFBPs (7,8,10); however, the cited studies did not determine whether tissue and secreted forms of IGFBPs differed in size, as was evident for IGFBP-2 and -3 in the present study. Research in sheep demonstrated that forms of IGFBP-2 and -3 in pituitary and stalk medium eminence tissue were smaller than those in serum (12,14,20), but these studies did not evaluate secretion of IGFBPs. Three potential N-linked glycosylation sites exist on IGFBP-3 (5), and the present study demonstrated that pituitary conditioned medium and serum have an increased predominance of more extensively glycosylated forms of IGFBP-3 than pituitary tissue.…”