Influence of splanchnic nerve on reserpine action in avian adrenal medulla

Catecholamine secretory vesicle stimulus-transcription coupling in vivo. Demonstration by a novel transgenic promoter/photoprotein reporter and inhibition of secretion and transcription by the chromogranin A fragment catestatin

Stimulation of chromaffin cell secretion in vitro triggers not only secretion but also resynthesis of just released catecholamines and chromogranin A, the precursor of the catecholamine release-inhibitory, nicotinic cholinergic antagonist peptide catestatin. Does stimulus-transcription coupling occur in vivo? And does catestatin antagonize secretion and transcription in vivo? To answer these questions, we employed a novel mouse strain harboring a chromogranin A promoter/firefly luciferase reporter transgene. Tissue-specific expression of the reporter was established by both luminescence and reverse transcription-PCR. Secretion and transcription in vivo were triggered by either direct nicotinic stimulation or vesicular transmitter depletion. Nicotinic blockade in vivo was attempted with either the classical antagonist chlorisondamine or the novel antagonist catestatin. Luciferase reporter expression was exquisitely sensitive over a large dynamic range, was specific for the transgenic animals, and paralleled typical neuroendocrine distribution of endogenous chromogranin A. Adrenal ontogeny revealed a rise of embryonic transgene expression until embryonal day 18, with an abrupt postnatal decline. Direct nicotinic stimulation of chromaffin cells caused catecholamine release and transgene transcription, each of which was nearly completely blocked by chlorisondamine. Similar adrenal results were obtained during vesicular catecholamine depletion. Both secretion and transcription were substantially blocked in the adrenal gland by catestatin. In brain and sympathetic nerve, stimulation of transcription was more modest, and reserpine responses were only incompletely blocked by chlorisondamine or catestatin, perhaps because of limited blood-brain barrier penetration by these cationic antagonists. Thus, nicotinic cholinergic stimulus-transcription coupling occurs in vivo and can be provoked either directly or indirectly (by vesicular transmitter depletion). Such coupling triggers the biosynthesis of chromogranin A, the precursor of catestatin. Catestatin itself blocks stimulation of both secretion and transcription in vivo. Thus, chromogranin A and its catestatin fragment may lie at the nexus of nicotinic cholinergic signaling in vivo.

Role of splanchnic nerve on steroid-hormone-induced alteration of adrenomedullary catecholamines in untreated and reserpinized pigeon

The aim of the present investigation was to ascertain (1) the effect of steroid hormones (corticosterone, dexamethasone, deoxycorticosterone, progesterone, testosterone and oestrogen) on the neural regulation of adrenomedullary catecholamine (CA) content, and (2) the neural modulation of the effect of glucocorticoid hormones (corticosterone and dexamethasone) on reserpine-induced resynthesis of CA. The experiment was conducted on unilaterally splanchnic-denervated pigeons. The findings revealed that 7 consecutive days of steroid treatments (2.5 mg.kg b.w.-1, i.m.) resulted in significant changes of CA content. Interestingly, the changes of epinephrine (E) content differed significantly between the innervated and denervated glands. This clearly indicates that the splanchnic nerve regulates steroid-induced alterations of E content in the pigeon. The results further revealed that the glucocorticoid hormones augmented reserpine-induced resynthesis of CA specifically in the innervated glands. This confirms that the splanchnic nerve is essential for the synergistic action of glucocorticoids and reserpine in accelerating resynthesis of CA.

Neural influence on oxytocin-induced changes of adrenomedullary catecholamines in the pigeon

Oxytocin (0.25 IU/100 g body wt) was injected intraperitoneally only once to unilaterally splanchnic denervated pigeons. The effects were investigated after 0.5, 4, 12, 24, 72, 144 and 216 h of administration. The findings revealed that oxytocin caused the release of more norepinephrine (NE) from the denervated glands up to 24 h after treatment. In contrast, oxytocin-induced release of epinephrine (E) showed no significant difference in between the innervated and the denervated glands after 0.5 h of treatment. Strikingly, oxytocin brought about release of more E from the denervated glands after 24 h of treatment. This indicates that the first phase of NE release and the second phase of E release are neurally regulated. The findings further revealed that the resynthesis of both NE and E was faster in the innervated glands after 216 h of oxytocin treatment. This clearly points out that the splanchnic nerve accelerates resynthesis of both NE and E induced by oxytocin.

Effect of insulin on serotonin, 5-hydroxyindole-acetic acid, norepinephrine, epinephrine and corticosterone contents in chick

Pineal serotonin (5-HT), 5-hydroxyindole-acetic acid (5-HIAA), norepinephrine (NE), epinephrine (E) and adrenal corticosterone, NE and E contents were measured spectrofluorometrically 5, 15, 30 and 60 min after insulin treatment to induce hypoglycemic stress. In the pineal gland, hypoglycemic stress caused dramatic decrease of 5-HT, resulted in initial decrease followed by an increase of 5-HIAA and brought about changes of NE and E. Corticosterone content in the adrenal gland increased significantly following treatment with insulin. Adrenal NE and E contents plummetted to control value followed by quick resynthesis. The findings indicate that insulin-induced hypoglycemia greatly modulates the activities of pineal and adrenal glands.

Neural modulation of lysine vasopressin-induced changes of catecholamines in the adrenal medulla of the pigeon

Lysine vasopressin was injected (0.25 IU/100 g body wt) intraperitoneally only once to unilaterally splanchnic denervated pigeons. Adrenomedullary catecholamine (CA) content was measured spectrofluorometrically 0.5, 4, 12, 24, 72, 144 and 216 h after administration. The findings revealed that in innervated glands, vasopressin caused 59-74% decrease of norepinephrine (NE) 4 and 24 h after administration while in denervated glands it resulted in 18-65% release of NE 0.5 to 144 h after injection. This indicates that the splanchnic nerve prevents early phase (up to 0.5 h) of vasopressin-induced release of NE. Vasopressin also caused decrease of Epinephrine (E) from both the innervated (68-73%) and denervated (69-74%) glands 0.5 and 4 h after injection indicating that the splanchnic nerve has no effect on vasopressin-induced release of E. Accelerated resynthesis of NE exceeding the control value (44-94%) was encountered 144 and 216 h after injection as compared to a slower increase (14%) in denervated glands 216 h after injection. Higher rate of resynthesis of E was encountered in the innervated glands 12 and 72 h after treatment. The findings clearly point out that the splanchnic nerve accelerates resynthesis of both NE and E induced by vasopressin.

Effect of stress on the catecholamine content of the adrenal gland of intact and bursectomized chicks

1. Bursa-intact and bursectomized chicks were exposed to cold-wet immobilization (CWI) stress for 1.5 min. The catecholamines (CA) from the adrenal gland were measured spectrofluorometrically 5, 15, 30 and 60 min after stress. 2. In bursa-intact chicks, the CWI stress caused decrease of both norepinephrine and epinephrine from the adrenal glands 5 min after stress. Resynthesis of epinephrine exceeded the control value 30 and 60 min after stress. 3. In bursectomized chicks, the CWI stress brought about a decrease of norepinephrine 15 and 30 min and of epinephrine 30 and 60 min after stress. 4. The findings suggest that bursa facilitates early (5 min) release of CA and also helps in quick resynthesis of epinephrine during stress.

Neural influence on the action of insulin in the adrenomedullary catecholamine content in the pigeon

Insulin-induced (4 IU/100 g b.wt.) changes of adrenomedullary catecholamines (CA) were investigated in unilaterally splanchnic denervated pigeons 0.5, 4, 12, 24, 72, 144 and 216 h after injection. Insulin caused depletion of more norepinephrine (NE) from the denervated glands 0.5 h after treatment. This indicates that the splanchnic nerve prevents early phase of insulin-induced depletion of NE. Accelerated resynthesis of NE exceeding the control value was more in the innervated glands 24 h after administration. Insulin brought about augmented synthesis of epinephrine (E) surpassing the control value in the innervated glands 72 h after treatment. The findings point out that the splanchnic nerve stimulates resynthesis of NE and synthesis of E induced by insulin.