Effects of ACTH and corticosteroids on phenylethanoIamine‐N‐methyltransferase (PNMT) expression as determined by immunocytochemical localization in the adrenal gland of the lizardPodarcis sicula

Abstract

This study was undertaken to investigate whether, in the lizard Podarcis sicula, the expression of adrenaline synthesizing enzyme phenylethanolamine-N-methyltransferase (PNMT) is influenced by variations in corticosteroid levels. Adrenal glands of specimens treated with ACTH or corticosteroids were collected and stained with avidin-biotin complex (ABC) and immunogold techniques, for light and electron microscopical observations, respectively. In non treated specimens, positive staining was mainly confined to the catecholamine containing cells (adrenaline cells), located closer to the steroidogenic ones. In treated specimens, instead, positive staining was found in all the cells of the ehromaffin portion of the gland (adrenaline and noradrenaline cells). Immunoelectron microscopy confirmed the distribution of immunoreactive cells observed at the light microscope. These results support the hypothesis that corticosteroids regulate PNMT expression in reptilian adrenal glands similarly to what occurs in mammals.

Release of aldosterone and catecholamines from the interrenal gland of Triturus carnifex in response to adrenocorticotropic hormone (ACTH) administration

“…Following ACTH administration in June, when almost exclusively noradrenaline granules were present in the chromaffin cells, together with the increase in noradrenaline release, we did not find any increase in the mean number of adrenaline granules in the chromaffin cells and/or in adrenaline serum level, as would be expected if PNMT enzyme were regulated by corticosteroids. In fact, in mammals and reptiles, ACTH administration enhances corticosteroid levels that in turn increase the activity of the enzyme that modifies the relative quantities of adrenaline and noradrenaline cells (Wurtman, 1966;Laforgia and Varano, 1978;Kent and Parker, 1993;Laforgia and Muoio, 1997;Hodel, 2001). Data are absent on the localization of the enzyme PNMT in the chromaffin cells of Triturus carnifex; however, preliminary studies by our research group (Capaldo et al, pers.…”

“…In reptiles PNMT is under the control of steroids secreted by the adrenal cortex (Laforgia and Varano, 1978;Laforgia and Muoio, 1997); in anuran amphibians PNMT is independent of the level of corticosteroids (Wurtman et al, 1968;Dupont et al, 1977), whereas data are absent for urodeles. Following ACTH administration in June, when almost exclusively noradrenaline granules were present in the chromaffin cells, together with the increase in noradrenaline release, we did not find any increase in the mean number of adrenaline granules in the chromaffin cells and/or in adrenaline serum level, as would be expected if PNMT enzyme were regulated by corticosteroids.…”

“…In contrast, ACTH was found to stimulate steroidogenesis (Callard and Callard, 1978;Lofts, 1978). In the lizard Podarcis sicula, ACTH administration enhances corticosteroid production, increasing PNMT activity and increasing the number of adrenaline-producing cells (Laforgia and Varano, 1978;Laforgia and Muoio, 1997). In fish, ACTH was shown to stimulate corticosteroid release from the interrenal cells of the head kidney Yaron, 1976, 1980;Gupta et al, 1985;Reid et al, 1998;Young, 1988) and an involvement in the control of catecholamine secretion in both the rainbow trout (Reid et al, 1996) and the Atlantic hagfish (Perry et al, 1993;Bernier and Perry, 1996) was found.…”

The adrenal gland of newt Triturus carnifex (Amphibia, Urodela) following in vivo betamethasone administration

“…In reptiles PNMT is under the control of steroids secreted by the adrenal cortex (Laforgia and Varano 1978;Laforgia and Muoio 1997); in anuran amphibians PNMT is independent of the level of corticosteroids (Wurtman et al 1968;Dupont et al 1976), whereas data are absent for urodeles. Further research is needed to verify the effect of corticosteroids on PNMT activity; however, to date our results of both ACTH and betamethasone administration seem to exclude a stimulation of PNMT enzyme by corticosteroids in T. carnifex, in agreement with the data obtained in anurans (Wurtman et al 1968;Dupont et al 1976).…”

Endothelin-B (ET B ) receptor distribution in tissues of the lizard Podarcis sicula

“…This catecholamine secretagogue effect of endothelins may have a marked relevance in the control of adrenal gland physiology. Evidence is available that intramedullary catecholamines exert a paracrine stimulatory control of the cortex function in many vertebrate species (Nussdorfer 1996;Laforgia and Muoio 1997).…”