Therefore, organisms have evolved mechanisms to tightly regulate blood perfusion and oxygenation, coordinate endocrine cell responses to secretory stimuli, and promote hormone uptake by blood vessels. To achieve this, endocrine cell activity and output has to be temporally correlated with changes in blood flow, resulting in the replenishment of cell energy stores and the coordinated passage of hormone into the vasculature. The generation of hormone pulses requires not only the energy demands of thousands of highly active endocrine cells to be met but also the temporally precise entry of hormone into the bloodstream. 1983, Giustina & Veldhuis 1998, Robinson & Hindmarsh 1999). The pulsatile pattern of secretion of most hormones, resulting in burst like or episodic increases in circulating concentrations, is necessary for the generation of an appropriate downstream physiological response as well as the regulation of target cell function in both health and disease ( Wildt et al. Finely tuned secretion of hormones is essential for regulating a multitude of basic body functions such as growth, metabolism, reproduction, and lactation.
