Decreased follicular steroids and insulin-like growth factor-I and increased atresia in diabetic gilts during follicular growth stimulated with PMSG

Abstract

Four streptozotocin-diabetic gilts (maintained on exogenous insulin for 3 months) and 4 normoglycaemic gilts were treated with 600 i.u. PMSG. Diabetic gilts had insulin therapy removed at the time of PMSG administration. Plasma glucose averaged 463 +/- 5 mg/100 ml for diabetic gilts and 82 +/- 4 mg/100 ml for control gilts over the 72-h sampling period. Serum insulin was lower in diabetic than in normoglycaemic gilts (glycaemic state by time interaction; P less than 0.0001). At ovary removal 75 h after PMSG, numbers and percentages of large (greater than or equal to 7 mm) and medium (3-6 mm) non-atretic follicles were similar for diabetic and control gilts (31 vs 68%; s.e.m. = 7; P less than 0.05). Diabetic gilts had a greater percentage of atretic follicles over all size classes (50 vs 21%; s.e.m. = 7; P less than 0.03). After PMSG, LH was suppressed within 12 h in control gilts and remained similar to values in diabetic gilts until 72 h, when LH was elevated in 2 diabetic gilts (glycaemic state by time interaction; P less than 0.001). Pulsatile LH patterns during 52-55 h after PMSG were not affected by glycaemic state. Serum concentrations of IGF-I tended (P less than 0.1) to be lower in diabetic gilts. Concentrations of oestradiol and FSH in serum were similar in diabetic and control gilts. Follicular fluid concentrations of oestradiol in follicles greater than or equal to 7 mm were lower in diabetic than normoglycaemic gilts (341 vs 873 ng/ml; s.e.m. = 86; P less than 0.05). Testosterone was higher in follicles 3-6 mm in diameter in diabetic than in normoglycaemic gilts (142 vs 80 ng/ml; s.e.m. = 26; P less than 0.05). Progesterone concentrations in follicular fluid were not affected by glycaemic state. Concentrations of IGF-I in follicles greater than or equal to 7 mm were lower in diabetic than control gilts (150 vs 200 ng/ml; s.e.m. = 13; P less than 0.05). We conclude that follicles of diabetic gilts respond to external gonadotrophic stimulation with decreased hormone production and increased ovarian follicular atresia, despite an absence of effects on circulating gonadotrophin and oestradiol concentrations.

Feed Restriction and Insulin Treatment Affect Subsequent Luteal Function in the Immediate Postovulatory Period in Pigs: Progesterone Production In Vitro and Messenger Ribonucleic Acid Expression for Key Steroidogenic Enzymes1

“…Insulin could support follicular development by reducing follicular atresia [23,24,43,44] and by suppressing follicular apoptosis [45]. Other in vivo studies also demonstrated that exogenous insulin treatment for 4 days in gonadotropintreated prepubertal gilts increased the number of follicles less than 3 mm in size [24], and maintained the 4-to 6-mm size follicle population in cyclic gilts when insulin treatment began on Day 15 of the cycle [23].…”

Feeding lactating primiparous sows to establish three divergent metabolic states: I. Associated endocrine changes and postweaning reproductive performance.

“…Indeed, LH has the ability to affect ovarian development directly (Cox and Britt, 1982;Rojanasthien et al, 1988;De Rensis et al, 1991). Local effects of insulin (Cox et al, 1987;Meurer et al, 1991) and nutrition (Flowers et al, 1988) on the number of follicles selected to ovulate have been established in gilts. However, the results of this experiment clearly indicate that the availability of additional nutrients during lactation did not increase ovulation rate or decrease the time to return to estrus.…”

Ovarian and hepatic insulin-like growth factor-I gene expression and associated metabolic responses in prepubertal gilts subjected to feed restriction and refeeding

“…Although plasma IGF-I concentrations and hepatic IGF-I gene expression have been shown to be affected by feeding level, it is not known whether fasting or feed restriction has the same effect on follicular fluid concentrations of IGF-I and on ovarian IGF-I gene expression in swine. There are, however, indications that decreased insulin levels may influence immunoreactive IGF-I levels within the ovaries of gilts and that this effect may be independent of gonadotrophins (Cox et al 1987;Meurer et al 1991). Cosgrove et al (1992) demon¬ strated that in chronically gonadotrophin-suppressed and feed-restricted gilts, refeeding was capable of stimulating ovarian development in the absence of an increase in gonadotrophin secretion.…”