Glucogenic supply increases ovulation rate by modifying follicle recruitment and subsequent development of preovulatory follicles without effects on ghrelin secretion

Abstract

This study determined the effects of short-term energy inputs on ghrelin secretion and possible links with changes in the follicle population or the ovulation rate. Oestrous cycle was synchronized in 16 Manchega sheep using progestagen sponges and cloprostenol. Half of the animals were treated from days 0 to 4 by the oral administration, twice daily, of 200 ml of a glucogenic mixture containing 70% of glycerol, 20% of 1,2-propanediol and 10% of water; the control group received 200 ml water. The mean (±s.e.m.) plasma glucose increased immediately after the first administration (3.9±0.3 vs 3.0±0.1 mmol/l in control group,P<0.05), remaining statistically different during the treatment. However, plasma ghrelin levels were similar in both groups. On the other hand, the results indicated that short-term energy inputs modify ovulation rate (1.9±0.1 vs 1.3±0.2 in control group,P<0.05) by increasing the number of follicles able to be selected to ovulate during the period of treatment (≥4 mm in size; 5.9±0.6 vs 4.3±0.4 at day 2,P<0.05). After sponge withdrawal, the number of these follicles decreased throughout follicular phase (5.8±0.8 to 1.5±0.4,P<0.0005) while the number of large follicles increased (≥6 mm in size; 0.8±0.4 to 2.0±0.3,P<0.05); this would indicate an active growth of preovulatory follicles that were not found in the control group. Thus, the increases of ovulation rate by high-energy inputs would be caused by an enhancement in the developmental competence of preovulatory follicles.