The neurohypophysial endocrine regulatory cascade: precursors, mediators, receptors, and effectors.

The neurohypophysial endocrine regulatory cascade has been described as a molecular model of neuroendocrine control of organismal functions. Any physiological function can be analyzed in molecular terms as a succession of interactions occurring either in a solution or in a membrane system. The key mechanism in the ordering of the cascade is the conformational recognition of the two partners at each step. Each interaction results in a change of conformation of a recognized protein that in turn becomes a recognizer for the following molecule. The cascade starts within the secretory cell by the processing of the expressed precursor along the secretory pathway until the storage of the mature mediator in vesicles and its subsequent exocytic secretion in blood. The circulating mediator recognizes the target cell through specific membrane receptors that transduce the message within this target cell. A second intracellular cascade leads to activation of the effector, the protein fulfilling the physiological function. The complexity of the messages is, in part, due to the duplication propensity of the genomic DNA, the frequent occurrence of multiple copies for precursors, mediators, receptors, and effectors, and therefore, a combinatorial diversity that increases during the course of evolution. Vertebrate neurohypophysial hormones can be ordered in two main evolutionary lineages, culminating in oxytocin and vasopressin in placental mammals. In this field, diversification of the messages was made by differential processing of the precursors, secondary gene duplications, the emergence of several types of receptors for each hormone, and a variety of effectors triggered by the second messengers within differentiated target cells. This review is an attempt to integrate neurohypophysial functions at the molecular, cellular, and organismal levels.