Immunocytochemical localization of substance P in the adrenal gland of Podarcis sicula (Reptilia, Lacertidae): evidence for its involvement in the modulation of adrenal activity

The autonomic nervous system and chromaffin tissue: neuroendocrine regulation of catecholamine secretion in non-mammalian vertebrates

If severe enough, periods of acute stress in animals may be associated with the release of catecholamine hormones (noradrenaline and adrenaline) into the circulation; a response termed the acute humoral adrenergic stress response. The release of catecholamines from the sites of storage, the chromaffin cells, is under neuroendocrine control, the complexity of which appears to increase through phylogeny. In the agnathans, the earliest branching vertebrates, the chromaffin cells which are localized predominantly within the heart, lack neuronal innervation and thus catecholamine secretion in these animals is initiated solely by humoral mechanisms. In the more advanced teleost fish, the chromaffin cells are largely confined to the walls of the posterior cardinal vein at the level of the head kidney where they are intermingled with the steroidogenic interrenal cells. Catecholamine secretion from teleost chromaffin cells is regulated by a host of cholinergic and non-cholinergic pathways that ensure sufficient redundancy and flexibility in the secretion process to permit synchronized responses to a myriad of stressors. The complexity of catecholamine secretion control mechanisms continues through the amphibians, reptiles and birds although neural (cholinergic) regulation may become increasingly important in birds. Discrete adrenal glands are present in the non-mammalian tetrapods but unlike in mammals, there is no clear division of a steroidogenic cortex and a chromaffin cell enriched medulla. However, in all groups, there is an obvious intermingling of chromaffin and steroiodogenic cells. The association of the two cell types may be particularly important in the amphibians and birds because like in mammals, the enzyme catalysing the methylation of noradrenaline to adrenaline, PNMT, is under the control of the steroid cortisol.

Histochemical distribution of endothelin-converting enzyme subtypes in Podarcis sicula (Squamata, Lacertidae) tissues

The distribution of endothelin-converting enzyme (ECE) in the lizard Podarcis sicula was investigated immunohistochemically using antibodies against endothelin-converting enzyme ECE-1 and endothelin-converting enzyme ECE-2 homologues. In all the tissues examined, immunoreactivity for both antibodies was found, although the distribution and degree of expression varied. Strong immunoreactivity was found in the endothelial cells and chromaffin tissue for both enzymes, whereas other tissues such as nervous tissue, renal tissue and hepatocytes display distinct patterns. Current knowledge does not allow correlation of these distribution patterns to specific functions but the data suggest that, in reptiles as in mammals, ECE is probably involved in physiological functions such as paracrine activity through endothelins and/or other substrates.