EFFECT OF VASOTOCIN AND ON OVIPOSITION IN THE HEN

J. RZ\l=A%k\SA and Z. EWY Department of Physiology, College of Agriculture, Krakow, Poland (Received Wth November 1969) Summary. Intravenous injection of vasotocin in the hen induced premature oviposition within a few minutes. The sensitivity of the oviduct both to vasotocin and oxytocin rose towards the time of normal oviposition. Vasotocin exhibited a much greater oviposition-inducing activity than oxytocin.

It is now established that oxytocin, and vasotocin are capable of stimulating the smooth muscle of the avian uterus. Oxytocin and vasotocin (8-arginine oxytocin) were found in the neurohypophysis of the hen (Chauvet, Lenci & Acher, 1960; Munsick, Sawyer & van Dyke, 1960) and from in vitro and in vivo studies, vasotocin was clearly the most potent oxytocic substance in this species (Munsick, Sawyer & van Dyke, 1960 ; Heller & Pickering, 1961; Ewy & Rzasa, 1968). Tanaka & Nakajo (1962a) reported a decrease in the content of vasotocin in the neurohypophysis of hens coincident with oviposition and suggested that the hormone was released into the blood and caused oviposition. Douglas & Sturkie (1964) and Sturkie & Lin (1966) assayed vasotocin in the blood of laying hens and found that the concentration of the hormone increased markedly a few minutes before oviposition, but returned to resting levels within 10 to 20 min after laying. It is known that injections of oxytocin and vasopressin cause premature expulsion of eggs in the hen (Tanaka & Nakajo, 1962b; Gilbert & Lake, 1963) and it was, therefore, of interest to examine the effect of the vasotocin on oviposition in the hen and to compare it with the effect of oxytocin. New Hampshire hens were maintained in individual cages and the time of their ovipositions was recorded from 07.00 hours to 16.00 hours for at least 4 weeks before any hen was selected for a test. All experiments were carried out to test for effects on the second or the terminal egg of a two- or three-egg clutch. We studied the effects of neurohypophysial hormones, injected intravenously (i.v.), on oviposition in hens with either a palpable hard-shell egg in utero (1 to 5 hr before the estimated laying time) or a soft-shell egg in utero (12 to 20 hr before the expected time of laying). The response of the hen was regarded as positive when oviposition was induced within 12 min after the injection. Synthetic oxytocin (450 oxytocic units/mg; Syntocinon, Sandoz) and synthetic vasotocin (250 pressor units/mg; Arginin Vasotocin, Sandoz) were used. 549

Downloaded from Bioscientifica.com at 09/28/2021 05:53:08AM via free access 550 J. Rzasa and Z· ^WJ The results obtained are presented in Table 1. Injections of vasotocin and oxytocin caused premature expulsion of eggs within a few minutes. The sensitivity of the uterus (shell gland) both to vasotocin and oxytocin rose towards the time of normal oviposition. In order to induce premature ovi¬ position 18 to 20 hr before the estimated laying time, a four-times greater dose ofvasotocin should be used than that injected 2 to 3 hr before the expected laying time. Effective doses of oxytocin were twenty times greater than those of vasotocin. Table 1 the effect of oxytocin and vasotocin on oviposition in the hen

Eggs prematurely Time before Drug used Dose No. laid Time of laying expected (fg/kg) birds after injection oviposition (hr) treated No. /o (min) 1 to 1¿ Oxy 1-0 8 100 5-7 2 to 3 Oxy 1-0 6 1 16-7 6-0 Oxy 2-0 6 6 100 3-7 AVT 0-1 10 10 100 3-5 3¿ to 5 Oxy 2-0 6 2 33-3 5-5 AVT 0-1 9 5 55-5 5-4 AVT 0-2 6 6 100 2-8 12 to 14 AVT 0-2 6 6 100 4-3 Oxy 4-0 6 3 50 4-5 18 to 20 AVT 0-2 5 1 20 5-0 AVT 0-4 5 5 100 1-9

Oxy = oxytocin, AVT = vasotocin. The types of egg obtained following the administration of neurohypophysial hormones at varying intervals before the estimated time of oviposition were : normal, hard-shelled eggs—1 to 3 hr; hard-shelled eggs, lacking pigment—3 to 5 hr; eggs with thin shells—12 to 14 hr; membranous eggs—18 to 20 hr. The synthetic vasotocin and oxytocin used in this study were kindly supplied by Sandoz Ltd, Basle, Switzerland. REFERENCES Chauvet, J., Lenci, M. T. & Acher, R. (1960) Présence de deux vasopressines dans la neurohypophyse du poulet. Biochim. biophys. Ada, 38, 571. Douglas, D. S. & Sturkie, P. D. (1964) Plasma levels of antidiuretic hormone during oviposition in the hen. Fedn Proc. Fedn Am. Socs exp. Biol. 23, 150. Ewy, Z. & Rzasa, J. (1968) Effect of vasotocin and oxytocin on contractility of the oviduct and on blood pressure in the hen. Ada physiol. pol. 19, 359. Gilbert, A. B. & Lake, P. E. (1963) The effect of oxytocin and vasopressin on oviposition in the domestic hen. J. Physiol., Lond. 169, 52p. Heller, H. & Pickering, B. T. (1961) Neurohypophysial hormones of non-mammalian vertebrates. J. Physiol., Lond. 155, 98. Munsick, R. ., Sawyer, W. B. & van Dyke, . B. (1960) Avian neurohypophysial hormones: pharmacological properties and tentative identification. Endocrinology, 66, 860. Sturkie, P. D. & Yu-Chong Lin (1966) Release of vasotocin and oviposition in the hen. J. Endocr. 35, 555. Tanaka, K. & Nakajo, S. (1962a) Participation of neurohypophysial hormone in oviposition in the hen. Endocrinology, 70, 453. Tanaka, K. & Nakajo, S. (1962b) Oviposition-inducing activities of the chicken posterior pituitary extract, synthetic oxytocin and mammalian vasopressin. XHth World's Poultry Congr., Sec. B, 123.

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