Neuromedins, smooth-muscle-stimulating peptides, are commonly divided into four groups: bombesin-like, kassinin-like, neurotensin-like and neuromedins U. In the present review, current data on the synthesis and mechanism of action of neuromedins on hypothalamo-pituitary-adrenal (HPA) axis will be presented. These neuropeptides and their receptors are localized to all components of the HPA axis, the only exemption seems to be neurokinin B, which is not detected in the adenohypophysis. Neuromedins exert a manifold effect on HPA axis, and their action on the adrenal suggests their involvement in the regulation of growth, structure and function of the adrenal cortex. Neuromedins may exert both direct and indirect effects on the adrenal cortex. Direct effect is proven by the stimulation of mineralo- and glucocorticoid output by isolated or cultured adrenocortical cells and by mobilisation of intracellular [Ca2+]i. Indirect effects, on the other hand, may be mediated by ACTH, arginine-vasopressin, angiotensin II, catecholamines or by other regulatory substances of medullary origin.

The effect of gonadectomy and gonadal hormone replacement on the activity of sterol ester hydrolase, steroid 5a-reductase and corticosterone output was studied in the adrenals of rats of both sexes.It was found that the specific activity of sterol ester hydrolase in 105,000 x g supernatant of the adrenal homogenates was higher in male than in female rats. On the contrary, corticosterone production by full adrenal homogenates, and adrenal steroid 5a-reductase activity was lower in male than in female rats.Eight weeks after orchiectomy no change in the activity of sterol ester hydrolase was found in the adrenal cortex, and testosterone replacement caused no appreciable differences in the enzymic activity as compared with the intact and orchiectomized animals. Ovariectomy resulted in an increase in the activity of sterol ester hydrolase whereas estradiol replacement caused a decrease in the enzymic activity to the level observed in the control group.In gonadectomized animals these changes accompanied an increase of steroid 5a-reductase activity in the adrenal glands, and after removal of the gonads no changes were found in corticosterone production by adrenal homogenates. Upon testosterone or estradiol replacement a substantial decrease in adrenal steroid 5a-reductase activity was noted.The results showed a marked sex difference in adrenal sterol ester hydrolase activity and indicate diverse effects of both testosterone and estradiol on various steps of steroidogenesis in rat adrenals.

The aim of the study was to investigate the cellular aspects of compensatory growth of the adrenal cortex of male hamster after unilateral adrenalectomy. Relative right adrenal gland weight was higher at 24 h after hemiadrenalectomy with no differences--if compared with sham operated hamsters--at 12, 48, 96 and 120 h. In vitro 3H-thymidine incorporation per mg of adrenal after 12 h was higher and 120 h lower in monoadrenalectomised male hamsters than in sham operated animals with no differences in the remaining time-points studied. If 3H-thymidine incorporation was expressed per entire gland, only 120 h after surgery the uptake was lower than in sham operated animals. Five days after hemiadrenalectomy an increase in the average volume of the zona fasciculata cell and no change in the glomerulosa and reticularis zones were observed. At that day solitary adrenal cortex contained similar number of parenchymal cells as the right adrenal gland of sham operated animals. Thus, hemiadrenalectomy in the male hamster leads to a prompt proliferative response of the contralateral gland at 12 h after surgery, followed by decreased proliferative activity at 120 h after surgery. Monoadrenalectomy increased average volume of the zona fasciculata cell and did not change the total number of parenchymal cells in the gland if compared with sham operated animals.

Adrenomedullin (AM) exerts a potent and long-lasting hypotensive effect and is considered to be an important hormone in blood pressure control. AM is a 52-amino-acid peptide synthesized as part of a 185-amino-acid preprohormone that also contains 20-amino-acid residues in the N-terminus, which has similar biological activity. This sequence is named a proadrenomedullin N-terminal 20 peptide (PAMP). Also, proadrenomedullin N-terminal peptide (PAMP)(12-20) exerts vasodepressor response, however this response is 3-fold less potent than the effect evoked by full-sequence peptide. Both AM and PAMP controls secretory activity of the pituitary gland and adrenal cortex, however, their action on the other endocrine glands is not recognized. Therefore, the aim of the study was to examine whether PAMP(12-20) is able to affect the structure and function of the rat thyroid gland. In adult female rats, subcutaneous PAMP(12-20) administration (1 or 4 nmol/rat/day for 6 days, autopsy 60 min after the last injection) had no effect on the weight of the thyroid gland. Peptide administration however, resulted in a dose-dependent increase in the volume of thyroid colloid, and lowered epithelium/colloid ratio in the gland (3.76 +/- 0.49, 2.66 +/- 0.27, 2.38 +/- 0.26, means +/- SE, n = 6, control, 1 and 4nmol PAMP/rat, respectively). PAMP administration changed neither the length of thyroid capillaries per unit area of surface nor their diameter. Lower dose of PAMP(12-20) significantly lowered blood TSH concentration (p < 0.01) while total and free T3 and T4 concentrations remained unchanged. Collectively, these findings suggest that PAMP(12-20) exerts a mild inhibitory effect on secretory activity of the rat thyroid gland.

The study aimed to examine the effects of pinealectomy (PX) and melatonin on adrenal cortex of orchiectomized rats and to explain whether the testosterone action on adrenal cortex is modified by the pineal gland. Neither PX (53 days) nor melatonin administration (10 days) had an effect on the structure as well as on the studied functional parameters of the adrenal gland--corticosterone output by homogenates, 11 beta-hydroxylase and 5 alpha-reductase activities, liver corticosterone metabolism and serum corticosterone level. On the contrary, PX of 14 months duration resulted in an increase in 5 alpha-reductase activity. Testosterone administration into orchiectomized rats lowered corticosterone output and liver corticosterone metabolism and these effects were unaffected by PX or melatonin. Testosterone lowered 5 alpha-reductase and 11 beta-hydroxylase activities, the effects not modified by PX, however, after melatonin administration activities of these enzymes were similar as in orchiectomized rats. Obtained results cast doubts on a physiological role of the pineal gland and its principal hormone--melatonin--in regulation of adrenocortical structure and secretory activity and suggest that testosterone action on the rat adrenal cortex is not modified by the pineal gland.