Thomas I. Koike

Arginine vasotocin (AVT) release in relation to uterine contractility in the hen

The relationship between plasma levels of arginine vasotocin (AVT) and factors associated with increases in uterine contractility was studied in the domestic hen. Plasma AVT levels increased from 3.3 +/- 0.3 microU/ml 15 min before a midsequence oviposition (OP) to 14.8 +/- 0.6 microU/ml at OP and then decreased to 5.2 +/- 0.6 microU/ml 15 min following OP. A ninefold increase in plasma AVT concentration was observed in hens laying a terminal egg of a sequence, which is not immediately followed by ovulation (OV). AVT levels also increased approximately 1 hr before the time of the first ovulation (C1OV) of the next sequence in association with an increase in uterine contractility. When OP was induced 2 hr before an expected OP by intrauterine administration of prostaglandin F2 alpha (PGF2 alpha, 1.0 microgram), plasma AVT levels immediately increased threefold (P less than 0.001) and then returned to basal levels within 30 min. In PGF2 alpha-treated hens AVT levels rose at the expected time of OP (P less than 0.05) in association with an increase in uterine contractility without OP actually occurring. When C1OV was induced by LH-RH (25 micrograms, iv), a small but significant increase of AVT similar to levels during spontaneous C1OV was observed. These results suggest that plasma AVT levels increase with every ovulation and oviposition in the absence of an egg in the uterus and that AVT is released in association with induced ovulation and oviposition.

Plasma levels of immunoreactive mesotocin and vasotocin during oviposition in chickens: Relationship to oxytocic action of the peptides in vitro and peptide interaction with myometrial membrane binding sites

Plasma concentrations of immunoreactive vasotocin (AVT) and mesotocin (MT) were measured periodically before and subsequent to spontaneous oviposition in conscious chickens. The concentrations of AVT and MT approximately an hour prior to oviposition were 5.2 +/- 1.1 microU/ml and 14.7 +/- 5.1 pg/ml, respectively. Plasma AVT levels increased abruptly at oviposition (25.1 +/- 3.3 microU/ml) and decreased to 5.0 +/- 0.6 microU/ml within 30 min postoviposition. Significant changes in MT were not observed. The data indicate that AVT is selectively released during oviposition. The uterus was removed immediately after oviposition and the oxytocic potencies of several peptides were tested on muscle strips in vitro. The order of oxytocic potencies was AVT greater than or equal to arginine vasopressin (AVP) much greater than MT = pressinoic acid. Partially purified membranes were prepared from separate portions of the uteri used in the oxytocic assay. [3H]arginine8 vasopressin, [3H]AVP, bound to membranes saturably (Bmax = 17 fmol/mg protein) and with high affinity (Kd = 0.7 nM). The rank order of potency of the peptides in displacing [3H]AVP from the binding sites was the same as in the oxytocic assay which suggests that the [3H]AVP binding sites in uterine membranes represent physiological receptors that interact with AVT during oviposition.

Effect of water deprivation of plasma radioimmunoassayable arginine vasotocin in conscious chickens (Gallus domesticus)

Abstract The effect of water deprivation on plasma immunoreactive arginine vasotocin levels ( P AVT ) was examined in conscious chicken. Dehydration for 96 hr was associated with reductions in body weight and increases in plasma osmolality ( P osm ) and P AVT . Consistent changes in hematocrit with dehydration were not observed. Maximum P AVT concentration (3.9 ± 0.47 μU/mI), observed after 72 hr of dehydration, was about six times greater than the basal value under normal hydration states. Changes in P AVT correlated significantly with increase in P osm , but did not correlate with changes in hematocrit.

Effect of saline infusion on plasma immunoreactive vasotocin in conscious chickens (Gallus domesticus)

Abstract Osmotic control of immunoreactive plasma vasotocin (PAVT) was examined in conscious White Leghorn pullets. The intravenous infusion of 1.0 M NaCl was associated with a fivefold increase in PAVT from a preinfusion average of 4.7 ± 2.0 μU/ml. No changes in vasotocin levels were observed in chickens infused with 0.154 M NaCl. A significant correlation was found between PAVT and plasma osmolality and plasma sodium concentration. Reductions in hematocrit and plasma protein concentration indicate that vascular volume was expanded by hyperosmotic saline infusion. The data suggest that a rise in plasma osmolality and/or sodium concentration stimulates AVT secretion in chickens.

An in situ hybridization and immunohistochemical study of vasotocin neurons in the hypothalamus of water-deprived chickens

The distribution of immunoreactive vasotocin (IR-AVT) and AVT mRNA in the hypothalamus of White Leghorn cocks was determined by immunohistochemistry and in situ hybridization, respectively. In control birds that were provided with water ad lib, AVT mRNA was distributed in the periventricular and lateral regions of the hypothalamus in clusters of neurons that correspond structurally with the mammalian paraventricular (PVN) and supraoptic (SON) nuclei. Although the distribution of AVT, identified by immunohistochemistry of adjacent serial sections within the hypothalamus, was similar to the distribution of AVT mRNA, the possibility that some positive staining was due to mesotocin neurons was not excluded. Water deprivation for 2 and 4 days resulted in both an increase in levels of AVT mRNA per neuron and the number of AVT mRNA-containing cells. Additionally, water deprivation resulted in a decrease in the amount of IR-AVT per neuron. The results indicate that osmotic stimulation increases AVT gene expression not only in individual neurons but also by activating subpopulation of neurons that are not observed in normally hydrated birds.

Plasma volume and electrolytes during progressive water deprivation in chickens (Gallus domesticus)

1. Studies were performed to examine the effects of progressive water deprivation in the fowl (Gallus domesticus). 2. A reduction in plasma volume and an increase in capillary permeability to protein were observed only after 3 or 4 days of dehydration. 3. Moderate changes in arterial blood pressure and heart rate were noted in dehydrated birds but respiratory rate and body temperature remained unchanged. 4. Dehydration was associated with increases in the concentration of total solutes, sodium and chloride in plasma but no changes were noted in plasma potassium levels or arterial pH. 5. The results indicate that the chicken can maintain volume more effectively during water deprivation than several mammalian species.

Arginine vasotocin and mesotocin levels in theca and granulosa layers of the ovary during the oviposition cycle in hens (Gallus domesticus)

Neurohypophysial hormones in mammals are synthesized by the ovary and may influence reproductive function. Although arginine vasotocin (AVT) can induce premature oviposition in chickens, the gonadal content of AVT or mesotocin (MT) has not been examined in this species. Ovarian follicles were removed 2 hr before oviposition (-2 hr), immediately after oviposition (0 hr), and 5 hr after oviposition (+5 hr). The theca and granulosa layers of the three largest preovulatory and postovulatory follicles were isolated, extracted, and assayed for immunoreactive AVT and MT. AVT content in the theca and granulosa layers was lowest at -2 hr and increased to maximum levels at +5 hr. Pre- and postovulatory follices contained similar amounts of AVT. Maximum AVT levels in the theca and granulosa layers were 2.5 +/- 0.6 and 1.3 +/- 0.2 ng/tissue, respectively. In contrast, theca content of MT was maximal at 0 hr and the highest peptide levels were observed in the largest preovulatory follicle (0.24 +/- 0.02 ng/tissue). The results demonstrate that, compared with circulating levels of the hormones, the ovary of the chicken contains high concentrations of AVT and MT. The ovarian content of AVT and MT varies in a different manner in relation to the oviposition cycle.

Interrelationship between arginine vasotocin, prostaglandin, and uterine contractility in the control of oviposition in the hen (Gallus domesticus).

Uterine electromyographic activity (EMG), plasma concentrations of prostaglandin (PG) F and E, and arginine vasotocin (AVT) were simultaneously measured in relation to PGE2-induced premature oviposition and to indomethacin-blocked oviposition in chickens. The administration of indomethacin (5 mg, im) 3 hr before the predicted time of oviposition delayed egg lay by 8-14 hr, whereas control hens laid eggs at the predicted time. In indomethacin-treated hens increases in uterine EMG activity and plasma concentrations of PGF, PGE, and AVT were not observed at the expected time of oviposition, whereas a marked increase in plasma PGF and AVT occurred during spontaneous oviposition. The intrauterine administration of PGE2 (1 microgram) 3 hr before predicted oviposition induced premature egg lay within 5 min. Premature oviposition was accompanied by significant elevations in both uterine EMG activity and plasma levels of AVT. Changes in plasma levels of PGF and PGE were not observed. When premature oviposition was induced, significant increases in EMG activity and plasma concentrations of PGF and AVT were observed at the expected time of oviposition in the absence of an egg in the uterus. The administration of PGE2 at the predicted time of oviposition in hens pretreated with indomethacin induced oviposition which was accompanied by a significant increase in plasma AVT levels. The results suggest that AVT release is stimulated by uterine contractility in chickens.

Arginine vasotocin gene expression in hypothalamic neurons is up-regulated in chickens drinking hypertonic saline: an in situ hybridization study.

Osmotic stress stimulates the release of the avian hypothalamic neuropeptide arginine vasotocin (AVT) into the peripheral circulation. We conducted the present study to investigate the effects of salt-loading on AVT secretion and AVT gene expression in specific hypothalamic nuclei in chickens. White Leghorn chickens were provided food ad lib and either water or 2% NaCl to drink. Both plasma osmolality and plasma AVT levels were significantly increased in chickens that drank 2% NaCl for either two or four days compared to that in chickens that drank water. Results from in situ hybridization analysis demonstrated an increase in the number of neurons expressing AVT mRNA in the supraoptic (SON) and paraventricular nuclei (PVN) in chickens provided 2% NaCl to drink compared to chickens that were provided water to drink. The number of grains per neuron increased in the PVN, but not in the SON of osmotically stimulated birds. Thus, increased osmolality resulting from ingestion of hypertonic saline is an effective stimulus to increase hypothalamic AVT mRNA content in chickens.

C-FOS EXPRESSION IN THE FOREBRAIN AND BRAINSTEM OF WHITE LEGHORN HENS FOLLOWING OSMOTIC AND CARDIOVASCULAR CHALLENGES

Abstract In chickens, hyperosmolality and hemorrhage increase hypothalamic vasotocin (AVT) gene expression and stimulate the secretion of AVT from the posterior pituitary gland. In this study, c-fos expression was used to identify areas in the forebrain and brainstem of the domestic chicken that are activated following acute osmotic stress and hemorrhage-induced hypotension. Conscious hens were osmotically stimulated by administering a single intraperitoneal injection of 3 M NaCl (5 ml/kg). Urethane-anesthetized hens were bled to a mean systemic arterial pressure of 80–90 mm Hg and maintained at this blood pressure for 1 h with additional bleedings as required. In both studies, the expression of c-fos was determined in control and experimental birds by using Northern blot analysis and in situ hybridization analysis. Osmotic stress and hemorrhage-induced hypotension increased c-fos expression in the same brain regions. Prominent structures in the forebrain that expressed c-fos mRNA following acute osmotic stress and hemorrhage-induced hypotension included the supraoptic nucleus and paraventricular nucleus and nuclei within the hypothalamus that are anterior and ventral to the third ventricle. In the chicken, this region includes the organum subseptale, the o. vasculosum laminae terminalis, and the nucleus septalis medialis. In the brainstem, following either injection of 3 M NaCl or hemorrhage-induced hypotension, increased c-fos expression was observed in the nucleus of the solitary tract, parabrachial nucleus, area postrema, and locus ceruleus. Thus, the chicken central nervous system appears to use shared neuronal circuitry to stimulate hypothalamic AVT release in response to disturbances in body fluid composition and decreases in either systemic blood pressure or volume.