Reproduction Abstracts

In the “KNDy hypothesis”, the latest concept explaining the control of GnRH secretion, the pulsatile GnRH signal is controlled by arcuate nucleus cells that produce kisspeptin (K), neurokinin B (N) and dynorphin (Dy). The interplay among these peptides involves one of them acting as a ‘pace-setter’, one as a ‘brake’, and the other as communicator of the final signal to the GnRH cells. To date the KNDy hypothesis has proven to be robust, but, if it is to persist, it needs to be able to explain acute changes in GnRH pulse frequency such as that evoked by metabolic signals. Metabolic status is a powerful regulator of reproductive activity – for example, an increase in food intake can stimulate testis function in male sheep. This response is mediated at least partly by an increase in GnRH pulse frequency that begins within a day of nutritional supplementation. For this response to offer an experimental model for challenging the KNDy hypothesis, we need a more precise measure of the rapidity of the increase in GnRH secretion after feed supplementation. We therefore studied sexually mature rams (n=24) that were acclimated to a diet designed to maintain constant bodyweight. On the day of experimentation, half the rams were given a supplement (150 g lupin grain). Blood was sampled from 8 h before feeding until 11 h after feeding. In supplemented rams, LH pulse frequency increased from 0.81±0.277 pulses per 8 h to 3.30±0.464 pulses per 8 h (P<0.001). In control rams, there was no change in pulse frequency (0.75±0.250 vs 1.95±0.644 pulses per 8 h; P>0.10). We have now begun using this model to test whether the KNDy cells are involved in nutrition-induced increases in frequency of GnRH pulses.