Asok Ghosh

Cytophysiology of the Avian Adrenal Medulla

Publisher Summary This chapter discusses the cytophysiology of the avian adrenal medulla. Birds are unique among homoiothermic vertebrates in possessing an adrenal gland in which cortical and medullary tissues are completely intermingled. In contrast, the eutherian adrenal gland is organized into layers: the central portion is medulla, and this compact organ is encapsulated by another organ, the adrenal cortex, which itself contains at least three concentric strata. The medulla releases two amines into circulation, adrenaline and noradrenaline. Extreme variation in the relative concentrations of these two hormones in the medulla is a unique feature of birds, among other vertebrates. In birds, noradrenaline appears to be an equally effective blood sugar-enhancing hormone as compared to adrenaline. A probable mechanism of avian noradrenaline action in the hyperglycemic response has been proposed. An almost equal effectiveness of both adrenaline and noradrenaline as pressor hormones has also been recorded in the avian group. The biosynthesis of catecholamines proceeds, possibly following the mammalian pattern, in the chromaffin cells: tyrosine → dopa → dopamine → noradrenaline → adrenaline. The chapter emphasizes on the important functional role played by the adrenal medulla in avian reproduction and bird migration. Several endocrine interactions with the avian adrenal medulla are also mentioned.

Influence of age and splanchnic nerve on the action of melatonin in the adrenomedullary catecholamine content and blood glucose level in the avian group

SummaryA single intraperitoneal (IP) melatonin injection (0.5 mg/100 g body wt.) caused an increase in norepinephrine (NE) fluorescence and elevation of NE content in newly-hatched pigeons (Columba livia), but a reduction of NE fluorescence and depletion of NE content in the adrenal medulla of newly-hatched crows (Corvus splendens) after 0.5 h of treatment. In contrast, in adults melatonin caused increase in NE fluorescence and elevation of NE content only in the parakeet (Psittacula krameri).Half an hour of IP melatonin treatment (0.5 mg/100 g body wt.) induced release of epinephrine (E) from the adrenal medulla of newly-hatched pigeon and parakeet. In contrast, in the adults melatonin caused more than a two-fold increase in E in the pigeon, and a significant increase in the crow.Single IP melatonin injection (0.5 mg/100 g body wt.) caused hypoglycemia in the newly-hatched parakeet and adult pigeon, and hyperglycemia in newly-hatched pigeon after 0.5 h of treatment. Melatonin failed to regulate glucose homoeostasis in newly-hatched and adult crow.Splanchnic denervation of the left adrenal gland was performed in the adult pigeon. The right adrenal served as the innervated gland. Melatonin-induced modulation of catecholamines following a single IP injection (0.5 mg/100 g body wt.) revealed significant increases in NE fluorescence and NE content at 4 and 12 h after treatment in the denervated gland only, which gradually approached normal levels 9 days after treatment. In contrast, E content showed more than a two-fold increase over the control value in both the innervated and denervated glands 0.5 and 24 h after treatment. At 9 days after treatment, E content showed significant depletion in the innervated gland.The results of this study indicate that melatonin modulates catechol hormone content in avian adrenal medulla, and also regulates glucose homoeostasis (except in the crow). The splanchnic nerve plays a vital role in the synthesis of NE but has no effect on E.

Probable role of androgen in the regulation of the uropygial gland

The hormonal regulation of the uropygial gland was investigated after administration of testosterone to adult pigeons of both sexes, by prepubertal castration in pigeons and ducks, and by postpubertal castration and replacement therapy of testosterone in adult castrate pigeons. The investigation was based on gravimetric, histological, and mitotic studies. Testosterone treatment elicited stimulation of the uropygial gland in intact birds. This has been accomplished by hyperplasia, accelerated cell differentiation (through lipogenesis), and moderate rise in cell loss. Prepubertal and postpubertal castration by surgical means provoked a depression in the activity of the uropygial gland. The glandular inactivity was evidenced by hypoplasia and retarded lipoidal output concomitant with accelerated rate of cell loss. Replacement with testosterone restored the gland to a normophysiological condition. It is concluded that androgen normally contributes to regulation of the uropygial gland in male birds.

Circadian rhythm in blood sugar and adrenomedullary hormonal concentrations in an avian and a reptilian species

The aim of the present investigation was to ascertain the circadian rhythm in the concentration of blood glucose and adrenal medullary hormones in the parakeet and the turtle. These substances were measured four times (0600, 1200, 1800, and 2400 hr) over a 24-hr period. The concentration of blood glucose and adrenal adrenaline and noradrenaline was higher during the day (0600 through 1800 hr) than that noted at night (2400 hr). The pattern of fluctuation was almost similar in both the animal species. The finding suggests that there is a clear circadian rhythm in the concentration of these substances in the parakeet and the turtle, and that this may be due to fluctuation in the activity of the animals.

Influence of splanchnic nerve on reserpine action in avian adrenal medulla

Reserpine at three doses (0.05, 0.2, and 0.8 mg/100 g body wt) has been injected intraperitoneally to seven unilaterally splanchnic denervated avian species, in order to ascertain the neural regulation of its action in avian adrenal medulla. The adrenomedullary catecholamines (CA) were estimated at 24 hr after reserpine injection. The findings revealed that reserpine at high doses caused 66-92% depletion of total CA from both the innervated and the denervated glands in all the species investigated. The low dose of reserpine in the passerine (common myna and bulbul) birds resulted in 40-84% reduction of both norepinephrine (NE) and epinephrine (E) from the adrenal glands irrespective of its nerve supply. As a contrast, it depleted 60-80% of both NE and E from the innervated glands as compared to 17-43% reduction from the denervated glands in nonpasserine (woodpecker, parakeet, and koel) birds. Interestingly, in other nonpasserine (pigeon and duck) birds, the low dose of reserpine depleted 66-71% of NE from the innervated glands as compared to only 2-13% reduction from the denervated glands. But in these birds, 60-85% depletion of E, however, occurred independent of neural regulation. The findings suggest that at high doses depletion of CA by reserpine is controlled by some nonneurogenic mechanisms. Generally speaking, at a low dose of reserpine, the splanchnic nerve probably modulates depletion of CA from the adrenal medulla of the nonpasserine birds while the same is governed by some nonneurogenic mechanisms in the passerine birds.

Effect of reserpine on the release of adrenomedullary catecholamines and their role in glycemic and pressor responses in two avian species

Abstract Reserpine in a dose of 0.75 mg/100 gm body weight injected into the fowl and the crow induced a significant fall in blood pressure after 20 hours. In both crow and fowl, hyperglycemia was noted after a period of 4 hours, but the crow showed a significant hypoglycemia after 20 hours. The blood sugar level declined in the fowl but remained higher than the control during this period. Reserpine treatment of shorter duration initiated a greater loss of noradrenaline (norepinephrine) in fowl and of adrenaline (epinephrine) in crow. A prolonged treatment with the tranquilizer caused a greater depletion of adrenaline than of noradrenaline in the fowl, while a similar stimulus in the crow resulted in a complete loss of both the catecholamines. The role of adrenomedullary hormones in avian carbohydrate metabolism and pressor homeostasis is discussed in the light of the present findings.

Influence of age on adrenomedullary catechol hormones content in twenty‐five avian species

Abstract Catechol hormones (Norepinephrine and Epinephrine) content in the adrenal medulla of 25 species of the newly‐hatched and adult birds were investigated. Norepinephrine (NE) and Epinephrine (E) were found to be the major hormones in the adrenal medulla of the newly‐hatched passerine and non‐passerine birds respectively. E was the preponderant hormone in the adrenal medulla of the adult passerine birds. The adrenal medulla of the adult non‐passerine birds produced either NE as the predominant catechol hormone or NE and E in almost equal proportion as the adrenomedullary hormones.

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.

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.