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GC Harris and HD Nicholson

Oxytocin (OT) is present in the mammalian testis and has been postulated to play a role in modulation of seminiferous tubule contractility. However, recent evidence suggests that the myoid cells responsible for such contractile activity do not express OT receptors. In this study computer-assisted analysis and time-lapse videomicrography were used to investigate the biological effects of neurohypophysial peptides and their analogues on seminiferous tubule contractility. Adult rat testes were placed in fresh oxygenated Dulbecco's modified Eagle's medium (DMEM) F12 medium, decapsulated and the tubules gently teased apart. A small section of tubule was placed in a microslide chamber and perifused with medium. Seminiferous tubules were treated with OT (2 nM), [Arg8]-vasopressin (AVP, 0.2 nM) or [Thr4,Gly7]-OT (TGOT, 2 nM, 8 nM and 0.2 microM). Specific antagonists were also given simultaneously with OT and AVP treatments. Data were analysed to give arbitrary units of contractility. Both OT and AVP increased tubule contractility, with AVP being at least 10 times more potent than OT. Treatment with the selective OT antagonist, desGly-NH2,d(CH2)5[d-Tyr2,Thr4]-ornithine vasotocin (OTA, 0.2 microM and 2 microM) significantly reduced OT-induced increases in seminiferous tubule contractility but had no effect on AVP-induced responses. In contrast, the AVP antagonist, Phaa-d-Tyr(Me)-Phe-Gln-Asn-Arg-Pro-Arg-Tyr-NH2 (AVPA) was more potent at reducing AVP-induced increases than OT-induced responses. The selective non-peptide AVPA SR 49059 blocked the response to both peptides in a similar manner, whilst the non-peptide OTA L367,773 did not block OT-induced increases in seminiferous tubule contractility at doses that were slightly inhibitory to AVP-induced responses. The specific OT agonist TGOT did not induce a contractile response. The data in this study demonstrate that in the testis AVP acts via V1a receptors to stimulate contractile activity and suggest that OT may act via a receptor which differs from the classical V1a and uterine-type OT receptor. These findings support a role for OT in the regulation of seminiferous tubule contractility and raise the possibility that AVP may also be important in this process.

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ME Guibbolini, PM Pierson and B Lahlou

Neurohypophysial hormone receptors and second messengers were studied in trout (Oncorhynchus mykiss) hepatocytes. Arginine vasotocin (AVT) and isotocin (IT) elicited a concentration-dependent inhibition of cAMP accumulation in the presence of 5x10(-8) M glucagon (maximal effect for 4.5x10(-7) M and 1.4x10(-7) M, half-maximal effect for 2.1x10(-8) M and 0.7x10(-8) M, AVT and IT respectively). The effect of glucagon was inhibited up to 90% by AVT and 80% by IT. While AVT inhibited (up to 50%) the basal cAMP production, IT had no such action. Specific V(1) or V(2) analogues (with reference to vasopressin in mammals) were used for pharmacological characterization of the type of neurohypophysial hormone receptor involved in this inhibition. The V(1) agonist [Phe(2), Orn(8)]-oxytocin inhibited the glucagon-stimulated cAMP production with a maximal effect for 6x10(-7) M and a half-maximal effect for 0.9x10(-8) M concentrations of the analogue. While the V(1) agonist reduced the glucagon-stimulated cAMP level by 70%, it showed only a tendency to reduce the basal level. The V(2) agonist [deamino(1), Val(4),d -Arg(8)]-vasopressin had no effect either on basal or on glucagon-stimulated cAMP production. The V(1) antagonist [d(CH(2))(5)(1), O-Me-Tyr(2), Arg(8)]-vasopressin totally reversed the 10(-8) M AVT-induced inhibition of 5x10(-8) M glucagon-stimulated cAMP production, whereas the V(2) antagonist [d(CH(2))(5)(1),d -Ile(2), Ile(4), Arg(8), Ala(9)]-vasopressin had no such effect. In this particular case, maximal and half-maximal effects of the V(1) antagonist were obtained for 2.3x10(-6) M and 1. 2x10(-6 )M respectively. Changes in intracellular calcium content were measured using the fluorescent probe FURA-2/AM. AVT and IT elicited a concentration-dependent increase in Ca(2+) accumulation. The comparison of the effect of 10(-8) M agonists versus AVT showed the following order of potency: AVT=IT>V(1) agonist>V(2) agonist. The V(1) antagonist reversed the AVT-induced Ca(2+) accumulation whereas the V(2) antagonist had no such effect. These results are taken as evidence for the presence in trout hepatocytes of neurohypophysial hormone receptors functionally close to the V(1a)-type linked to cAMP production and Ca(2+) mobilization.

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R W Carón, G A Jahn and R P Deis

Abstract

We studied the capacity of different GH preparations, natural human (h)GH, recombinant hGH (rhGH), rat (r)GH, ovine (o)GH, bovine (b)GH and porcine (p)GH, and ovine prolactin (oPRL), to stimulate lactogenesis in ovario-hysterectomized pregnant rats or intact lactating rats treated with bromocriptine (BC). Ovariohysterectomy (OVX-HYS) performed at 0800 h on day 19 of pregnancy induced lactogenesis, i.e. increases in mammary casein and lactose and positive response to the oxytocin test, 28 h later. Lactogenesis was prevented by treatment with BC (1·5 mg/kg) immediately after surgery (OVX-HYS-BC). The hormones were given at doses of 0·25 or 0·5 mg/rat (except rhGH given only at 0·5 mg/rat) at 1200 and 2000 h on day 19. Casein was increased by both doses of oPRL and hGH, rhGH and 0·25 mg oGH, and lactose by both doses of oPRL, rhGH and 0·25 mg rGH. The other GH preparations had no effect. The oxytocin test demonstrated the presence of milk in the mammary tissues of the OVX-HYS rats and in the OVX-HYS-BC plus oPRL (0·25 and 0·5 mg) or rhGH-treated groups.

Injection of BC to pregnant rats at 2000 h on day 20 and at 0800 h on day 21 decreased litter growth on the first 4 days postpartum. Two-thirds of the litters resumed growth after day 4, indicating the recuperation of milk production, while the rest never recuperated. Serum prolactin in BC-treated rats was reduced until day 4 postpartum. On day 6 the rats which had recuperated had normal values, while those which had still not recuperated had lower values. BC-treated rats were injected s.c. with 0·25 mg each of oPRL, hGH, rGH, oGH, bGH or pGH, or 0·25 or 0·5 mg rhGH/rat, immediately postpartum and 12, 24 and 36 h later. hGH and 0·5 mg rhGH induced levels of milk production similar to controls except on day 3. oPRL and rhGH (0·25 mg), induced a partial reversion of the effect of BC. rGH and oGH had a slight effect on days 1 and 2 and all the litters resumed growth on day 7. In contrast, pGH and bGH were inactive.

The affinity of hGH for the prolactin receptor, measured as displacement of 125I-labelled oPRL binding to crude liver membranes, was comparable with that of oPRL. While rhGH was ten times less active than oPRL, rPRL was 100 times lower and all the other GH preparations had at least 104 times lower capacity to displace 125I-labelled oPRL.

These results indicate that both natural and recombinant hGHs are potent inductors of milk synthesis in pregnant or lactating rats, most probably due to their actions at the level of the prolactin receptor. rGH and oGH have a partial action, while pGH and bGH seem to be inactive. The actions of non-human GHs may be explained by their somatogenic properties exclusively, and indicate that GH may play a role in the optimization of milk production during lactation and an accessory role in the induction of lactogenesis in pregnant rats.

Journal of Endocrinology (1994) 142, 535–545

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M P Arpin-Bott, E Waltisperger, M J Freund-Mercier and M E Stoeckel

Abstract

The localization of oxytocin (OT)-binding sites in the developing rat kidney and their pharmacological characterization were investigated by means of autoradiographic techniques. The cellular localization was studied by application of the histoautoradiographic technique to (1) frozen sections and semithin sections from kidney slices incubated in vitro in the presence of a 125I-labelled OT antagonist and (2) frozen and semithin sections from kidneys after in vivo systemic infusion of the radioligand. Pharmacological characteristics were determined in competition experiments by using quantitative film autoradiography.

Specific OT-binding sites were first detected at embryonic day 17 (E17) in the cortex. At early stages up to postnatal days (PN30), the cortical OT-binding sites were highly concentrated on the juxta- and paraglomerular portion of the distal tubule; in the adult they were restricted to the macula densa. In the medulla, OT-binding sites were first detected at E19 when this region is forming; they were localized on the thin limb of Henle's loop. These data obtained by in vitro binding were confirmed by in vivo binding at PN30 which showed, in addition, the presence in one rat of OT-binding sites in the inner stripe of the outer medulla.

At all stages examined (PN15 to PN90), cortical OT-binding sites had a higher selectivity for OT versus vasopressin (IC50=0·78 ± 0·04 nm and 8 ± 0·5 nm respectively at PN90) than medullary sites (IC50= 1·9 ± 0·27 nm and 2±1·13 nm respectively at PN90). These data suggest that the OT-binding sites of the macula densa and thin Henle's loop, detected in the rat kidney, represent two subtypes of OT receptors which could mediate distinct effects of OT on kidney function.

Journal of Endocrinology (1997) 153, 49–59

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MP Wijayagunawardane, A Miyamoto, Y Taquahashi, C Gabler, TJ Acosta, M Nishimura, G Killian and K Sato

The precise regulatory mechanisms of cyclic oviductal contraction in the cow are unclear. The purpose of this study was to evaluate the effect of luteinizing hormone (LH), steroids, prostaglandins (PGs) and peptides on the oviductal contraction and secretion of PGs and endothelin (ET-1). In addition, the cyclic expression of mRNA for ET-1 and its receptors (ET-R) was evaluated by reverse transcription-polymerase chain reaction (RT-PCR). In the in vitro microdialysis study, an infusion of LH alone or in combination with progesterone (P(4)), estradiol-17beta (E(2)) and/or ET-1 stimulated pronounced release of PGE(2), PGF(2alpha) and ET-1 in the oviducts from cows in the follicular and postovulatory phases. The addition of LH, LH+P(4)+E(2) and/or ET-1 to the medium increased the amplitude of oviductal contraction. However, oxytocin (OT) completely blocked the responses of oviductal secretion and contraction. In contrast, these substances did not show any effect in the oviducts from cows in the mid luteal phase. Similar expression patterns of mRNA encoding for ET-R type A and type B were found, which were highest during the postovulatory phase, lower during the luteal phase, with the lowest expression during the follicular phase. We suggest that the preovulatory LH surge, together with increasing E(2) levels from the Graafian follicle and a basal P(4) from regressing corpora lutea (CL), stimulates maximum oviductal production of PG and ET-1, resulting in oviductal contraction for a rapid transport of gametes. OT released from the newly-formed CL may block these mechanisms, and slow contractions for transport of the embryo to the uterus.

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H. Ikegami, H. Jikihara, K. Koike, K. Morishige, H. Kurachi, N. Yamamoto, K. Hirota, A. Miyake and O. Tanizawa

ABSTRACT

The administration of thyrotrophin-releasing hormone (TRH) causes a variety of dopamine-related biological events. To understand the specific role of TRH on rat hypothalamic dopamine neurones, we examined the in-vivo effects of intraventricular (i.c.v.) infusion of TRH on the release and synthesis of prolactin in the rat pituitary gland and on the changes in binding of [3H]MeTRH and dopamine turnover rates in rat hypothalamus. We have also examined the in-vitro effects of TRH on the release of [3H]dopamine from dispersed tuberoinfundibular dopamine neurones.

Female rats were treated with i.c.v. infusions of 1 μmol TRH/l daily for 1, 3 and 7 days using Alzet osmotic pumps. Following 7 days of treatment the serum prolactin concentrations were significantly decreased. A reduction in hypothalamic TRH-binding sites (Bmax) was also apparent but the dissociation constant (K d) was unaffected. Northern blot analysis of total RNA isolated from the pituitary glands of control animals using 32P-labelled prolactin cDNA as a probe indicated the presence of three species of prolactin gene transcripts of approximately 3·7, 2·0 and 1·0 kb in size, and these were decreased by TRH treatment. We examined the turnover rate of dopamine in the rat hypothalamus when TRH was administered i.c.v. for 7 days. There was a significant increase in 3,4-dihydroxyphenylacetic acid/dopamine ratio with TRH treatment. Moreover, exposure to TRH stimulated [3H]dopamine release from rat tuberoinfundibular neurones in a time- and dose-dependent manner. Dopamine receptor antagonists such as SCH23390 and (−)sulpiride, and other neuropeptides such as vasoactive intestinal peptide and oxytocin did not affect TRH-stimulated [3H]dopamine release.

These data suggest that i.c.v. administration of TRH might decrease both prolactin secretion and accumulation of prolactin gene transcripts in the pituitary by stimulating dopamine release from tuberoinfundibular neurones.

Journal of Endocrinology (1992) 133, 59–66

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AV Sirotkin, AV Makarevich, HB Kwon, J Kotwica, J Bulla and L Hetenyi

The aims of this study on porcine ovarian granulosa cells were to examine the effect of GH on oxytocin (OT), IGF-I and IGF-I receptors, IGF-binding protein-3 (IGFBP-3), progesterone and prostaglandin E (PGE), as well as to determine whether IGF-I and/or OT may be mediators of GH action. The cells were cultured either with porcine GH (pGH) (1 ng/ml to 10 microg/ml or 100 ng/ml only), antiserum against IGF-I (0.1%), antiserum against OT (0.1%) or a combination of GH (10 ng/ml) with antiserum against IGF-I or antiserum against OT (0.1%). The secretion of IGF-I, OT, IGFBP-3, progesterone and PGE was determined using RIA/IRMA, whilst the IGF-I binding sites were measured using a radioreceptor assay. It was observed that pGH increased the secretion of IGF-I and the abundance of IGF-I binding sites in granulosa cells. Furthermore, GH inhibited OT release, stimulated progesterone and PGE output, but had no significant effect on IGFBP-3 secretion. Immunoneutralization of IGF-I by antiserum against IGF-I inhibited PGE secretion, but it did not influence progesterone or IGFBP-3 secretion. Binding of OT by antiserum suppressed IGFBP-3, PGE, but not progesterone secretion. Neither immunoneutralization of IGF-I nor OT substantially prevented the effects of GH on progesterone, IGFBP and PGE. These observations demonstrate the involvement of GH, IGF-I and OT in the control of porcine ovarian secretory activity and the ability of GH to regulate IGF-I and OT production and IGF-I reception. Nevertheless, lack of correlation between the effects of GH, antiserum against IGF-I and antiserum against OT, as well as the inability of blockade of IGF-I or OT to prevent the effects of GH, suggests that IGF-I and OT, despite their dependence on GH, do not mediate GH action on ovarian cells.

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T Engstrøm, P Bratholm, H Vilhardt and N J Christensen

Abstract

The altered myometrial contractile activity near term of pregnancy is partly due to changes in the responsiveness to catecholamines. Previous experiments have basically been concerned with uterine adrenoceptor binding characteristics. In the present study we have evaluated total myometrial DNA, β2-adrenoceptor mRNA and isoproterenol-induced relaxation of rat isolated uterine strips pre-contracted with potassium on days 0, 7, 14 and 21 of pregnancy and on day 5 post-partum. Total myometrial DNA expressed per milligram wet tissue peaked at day 14 of pregnancy followed by a decrease at the end of gestation. This suggests that hyperplasia predominates in the growth of the uterus in early gestation, whereas hypertrophy may be more marked in late pregnancy. The concentration of β2-adrenoceptor mRNA decreased linearly throughout the gestational period (0·73 ± 0·20 amol/mg wet tissue on day 0 vs 0·34 ± 0·09 amol/mg wet tissue on day 21, P<0·05). Five days after parturition, at which time the uterus had returned to its pre-pregnant weight, β2-adrenoceptor mRNA was found to have increased 8-fold (2·79 ± 0·14 amol/mg wet tissue, P<0·05) as compared with day 21. The maximal effect of isoproterenol on pre-contracted uterine strips in which α-receptors were blocked by phentolamine showed a similar decrease which on day 21 reached 67% of the day 0 level (P<0·001). EC50 values were unchanged in all groups except day 21 pregnant rats in which an increase was observed. One-way ANOVA with Bonferroni's t-test showed statistically significant differences only between the day 21 group and either the day 5 post-partum group or the day 14 pregnant group (P<0·05).

The observed alteration in EC50 prior to the end of gestation indicates that the system becomes less sensitive to β2-adrenergic stimulation at this time. We conclude that a reduction of de novo synthesis of β2-adrenoceptors may play a role in contributing to the increased myometrial activity at term. We further suggest that the dramatic up-regulation of β2-adrenoceptor mRNA postpartum may protect the fully involuted uterus against excessive contractions induced by oxytocin secreted during lactation.

Journal of Endocrinology (1997) 153, 393–399

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Donald Pfaff

multiplicative set of gene inductions allows the female to participate in reproductive behaviour sequences. Anxiety reduction The oxytocin gene and the gene for its receptor are both expressed by hypothalamic neurons at

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F Lucio-Oliveira and C R Franci

. doi:10.1016/0024-3205(86)90638-7 . Gutkowska J Jankowski M Lambert C Mukaddam-Daher S Zingg HH McCann SM 1997 Oxytocin releases atrial natriuretic peptide by combining with oxytocin receptors in the heart . PNAS 94 11704 – 11709