ABSTRACT
This chapter assesses from a comparative point of view, the present state of our knowledge concerning the aminergic and peptidergic factors involved in the regulation of the pars intermedia. Rapid and delicate regulation of the secretory activity of the pars intermedia is of prime importance in cold-blooded vertebrates. The pars intermedia of the pituitary has been described as a “compact, almost avascular structure exhibiting an abundant and diffuse innervation”. The intermediate lobe of the pituitary synthesizes a multifunctional glycoprotein, called pro-opiomelanocortin (POMC), which gives rise, through specific processing to a variety of bioactive peptides. In all vertebrates examined so far, with the exception of lizards, the pars intermedia is profusely innervated by fibers coursing between the parenchymal cells. Several classical neurotransmitters, other than dopamine, noraurenaline GABA, and serotonin, have been reported to be implicated in the regulation of melanotropin release. Interactions between thyrotropin-releasing hormone and various hormones, neuropeptides, or neurotransmitters on melanotropin secretion, have been examined.
