Gonadotrophic, prolactin, corticosterone, and gonadal hormones levels over 15 months in Giant Amazon River Turtles - Podocnemis expansa (Schweigger, 1812) (Testudines: Podocnemididae), in captive conditions / Gonadotrofinas, prolactina, corticosterona, e as hormonas sexuais durante 15 meses de Tartarugas da Amazônia - Podocnemis expansa (Schweigger, 1812) (Testudines: Podocnemididae), em condições de cativeiro

Abstract In order to achieve successful captive breeding the Podocnemis expansa, it is necessary to study their reproductive endocrinology. The purpose of this research was to evaluate and characterize plasma concentrations in gonadotrophic, gonadic, corticosterone and prolactin hormones from Giant Amazon Turtles under captive conditions. Blood samples were collected over a 15 month period. The samples were assayed by the use of radioimmunoassay, prolactin, corticosterone, LH, FSH, testosterone, 17β-estradiol and progesterone. We verified significant seasonal pattern increase in 17β-estradiol levels and decrease in progesterone levels in the course of a year, which indicates vitellogenesis. This is related to normal ovarian cycles and possibly to the functional integrity of the hypothalamus-pituitary-gonad axis of captive females. There were negative correlations between testosterone and corticosterone in the male samples, suggestive of stress (management stress) on the reproductive system. The plasma concentrations of gonadotrophic, gonadic, prolactin and corticosterone hormones may be used as a reference for further research and possible therapeutic approaches. The data collected during this research are unprecedented for this species and may serve as a reference for future research regarding the reproductive cycle of this turtle, also allowing reproductive management while in captivity. Information about these hormones must be gathered from wild populations during different periods of the year for better clarification of the reproductive physiology of this species.

Resumo Com o objetivo de obter reprodução em cativeiro de Podocnemis expansa, é necessário reunir o conhecimento a respeito de sua endocrinologia reprodutiva. O objetivo deste trabalho foi avaliar e caracterizar as concentrações plasmáticas de hormônios gonadotróficos, gonadais, corticosterona e prolactina em Tartarugas da Amazônia em condições de cativeiro. Amostras de sangue foram coletadas durante 15 meses. As amostras foram ensaiadas pelo uso de um radioimunoensáio, prolactina, corticosterona, LH, FSH, testosterona, 17β-estradiol e progesterona. Verificou-se aumento de padrão sazonal significativo nos níveis de 17β-estradiol e diminuição dos níveis de progesterona ao longo do ano, o que indica o recrutamento folicular. Isto está relacionado com ciclos ovarianos normais e possivelmente para a integridade funcional do eixo hipotálamo-hipófise-gônadas de fêmeas em cativeiro. Houve correlação negativa entre testosterona e corticosterona nas amostras do sexo masculino, sugestivos de efeito do estresse de manejo sobre o sistema reprodutivo. As concentrações plasmáticas de hormônios gonadotrofinas, gonadais, prolactina e hormônios corticosterona pode ser usado como referência para futuras pesquisas e possíveis abordagens terapêuticas. Os dados médios coletados durante a pesquisa são inéditos para a espécie e pode servir como referência para futuras pesquisas sobre o sistema reprodutivo da tartaruga, também permitindo manejo reprodutivo em cativeiro. Informações sobre esses hormônios devem ser recolhidas a partir de natureza selvagem em diferentes períodos do ano para melhor esclarecimento da fisiologia da reprodução desta espécie.

Social condition affects hormone secretion and exploratory behavior in rats

Studies of behavior, endocrinology and physiology have described experiments in which animals housed in groups or in isolation were normally tested individually. The isolation of the animal from its group for testing is perhaps the most common situation used today in experimental procedures, i.e., there is no consideration of the acute stress which occurs when the animal is submitted to a situation different from that it is normally accustomed to, i.e., group living. In the present study, we used 90 male 120-day-old rats (Rattus norvegicus) divided into 5 groups of 18 animals, which were housed 3 per cage, in a total of 6 cages. The animals were tested individually or with their groups for exploratory behavior. Hormones were determined by radioimmunoassay using specific kits. The results showed statistically significant differences between testing conditions in terms of behavior and of adrenocorticotrophic hormone (ACTH: from 116.8 ñ 15.27 to 88.77 ñ 18.74 when in group and to 159.6 ñ 11.53 pg/ml when isolated), corticosterone (from 561.01 ñ 77.04 to 1036.47 ñ 79.81 when in group and to 784.71 ñ 55.88 ng/ml when isolated), luteinizing hormone (from 0.84 ñ 0.09 to 0.58 ñ 0.05 when in group and to 0.52 ñ 0.06 ng/ml when isolated) and prolactin (from 5.18 ñ 0.33 to 9.37 ñ 0.96 when in group and to 10.18 ñ 1.23 ng/ml when isolated) secretion, but not in terms of follicle-stimulating hormone or testosterone secretion. The most important feature observed was that in each cage there was one animal with higher ACTH levels than the other two; furthermore, the exploratory behavior of this animal was different, indicating the occurrence of almost constant higher vigilance in this animal (latency to leave the den in group: 99.17 ñ 34.95 and isolated: 675.3 ñ 145.3 s). The data indicate that in each group there is an animal in a peculiar situation and its behavior can be detected by ACTH determination in addition to behavioral performance.

Is the infertility in hypothyroidism mainly due to ovarian or pituitary functional changes?

The objective of the present study was to examine whether hypothyroidism affects the reproductive system of adult female rats by evaluating ovarian morphology, uterus weight and the changes in serum and pituitary concentrations of prolactin and gonadotropins. Three-month-old female rats were divided into three groups: control (N = 10), hypothyroid (N = 10), treated with 0.05 percent 6-propyl-2-thiouracil (PTU) in drinking water for 60 days, and T4-treated group (N = 10), receiving daily sc injections of L-thyroxine (0.8 æg/100 g body weight) during the last 10 days of the experiment. At the end of 50 days of hypothyroidism no hypothyroid animal showed a regular cycle, while 71 percent of controls as well as the T4-treated rats showed regular cycles. Corpora lutea, growing follicles and mature Graafian follicles were found in all ovaries studied. The corpora lutea were smaller in both the hypothyroid and T4-replaced rats. Graafian follicles were found in 72 percent of controls and only in 34 percent of hypothyroid and 43 percent of T4-treated animals. Serum LH, FSH, progesterone and estradiol concentrations did not differ among the three groups. Serum prolactin concentration and the pituitary content of the three hormones studied were higher in the hypothyroid animals compared to control. T4 treatment restored serum prolactin concentration to the level found in controls, but only partially normalized the pituitary content of gonadotropins and prolactin. In conclusion, the morphological changes caused by hypothyroidism can be a consequence of higher prolactin production that can block the secretion and action of gonadotropins, being the main cause of the changes observed

Role of the hypothalamic pituitary adrenal axis in the control of the response to stress and infection

The release of adrenocorticotropin (ACTH) from the corticotrophs is controlled principally by vasopressin and corticotropin-releasing hormone (CRH). Oxytocin may augment the release of ACTH under certain conditions, whereas atrial natriuretic peptide acts as a corticotropin release-inhibiting factor to inhibit ACTH release by direct action on the pituitary. Glucocorticoids act on their receptors within the hypothalamus and anterior pituitary gland to suppress the release of vasopressin and CRH and the release of ACTH in response to these neuropeptides. CRH neurons in the paraventricular nucleus also project to the cerebral cortex and subcortical regions and to the locus ceruleus (LC) in the brain stem. Cortical influences via the limbic system and possibly the LC augment CRH release during emotional stress, whereas peripheral input by pain and other sensory impulses to the LC causes stimulation of the noradrenergic neurons located there that project their axons to the CRH neurons stimulating them by alpha-adrenergic receptors. A muscarinic cholinergic receptor is interposed between the alpha-receptors and nitric oxidergic interneurons which release nitric oxide that activates CRH release by activation of cyclic guanosine monophosphate, cyclooxygenase, lipoxygenase and epoxygenase. Vasopressin release during stress may be similarly mediated. Vasopressin augments the release of CRH from the hypothalamus and also augments the action of CRH on the pituitary. CRH exerts a positive ultrashort loop feedback to stimulate its own release during stress, possibly by stimulating the LC noradrenergic neurons whose axons project to the paraventricular nucleus to augment the release of CRH.

Antisense mRNA for NPY-Y1 receptor in the medial preoptic area increases prolactin secretion

We investigated the participation of neuropeptide Y-Y1 receptors within the medial preoptic area in luteinizing hormone, follicle-stimulating hormone and prolactin release. Four bilateral microinjections of sense (control) or antisense 18-base oligonucleotides of messenger ribonucleic acid (mRNA) (250 ng) corresponding to the NH2-terminus of the neuropeptide Y1 receptor were performed at 12-h intervals for two days into the medial preoptic area of ovariectomized Wistar rats (N = 16), weighing 180 to 200 g, treated with estrogen (50 µg) and progesterone (25 mg) two days before the experiments between 8.00 and 10:00 a.m. Blockade of Y1 receptor synthesis in the medial preoptic area by the antisense mRNA did not change plasma luteinizing hormone or follicle-stimulating hormone but did increase prolactin from 19.6 + or - 5.9 ng/ml in the sense group to 52.9 + or - 9.6 ng/ml in the antisense group. The plasma hormones were measured by radioimmunoassay and the values are reported as mean + or - SEM. These data suggest that endogenous neuropeptide Y in the medial preoptic area has an inhibitory action on prolactin secretion through Y1 receptors

Neuroendocrine regulation of salt and water metabolism

Neurons which release atrial natriuretic peptide (ANPergic neurons) have their cell bodies in the paraventricular nucleus and in a region extending rostrally and ventrally to the anteroventral third ventricular (AV3V) region with axons which project to the median eminence and neural lobe of the pituitary gland. These neurons act to inhibit water and salt intake by blocking the action of angiotensin II. They also act, after their release into hypophyseal portal vessels, to inhibit stress-induced ACTH release, to augment prolactin release, and to inhibit the release of LHRH and growth hormone-releasing hormone. Stimulation of neurons in the AV3V region causes natriuresis and an increase in circulating ANP, whereas lesions in the AV3V region and caudally in the median eminence or neural lobe decrease resting ANP release and the response to blood volume expansion. The ANP neurons play a crucial role in blood volume expansion-induced release of ANP and natriuresis since this response can be blocked by intraventricular (3V) injection of antisera directed against the peptide. Blood volume expansion activates baroreceptor input via the carotid, aortic and renal baroreceptors, which provides stimulation of noradrenergic neurons in the locus coeruleus and possibly also serotonergic neurons in the raphe nuclei. These project to the hypotlalamus to activate cholinergic neurons which then stimulate the ANPergic neurons. The ANP neurons stimulate the oxytocinergic neurons in the paraventricular and supraoptic nuclei to release oxytocin from the neural lobe which circulates to the atria to stimulate the release of ANP. ANP causes a rapid reduction in effective circulating blood volume by releasing cyclic GMP which dilates peripheral vessels and also acts within the heart slow its rate and atrial force of contraction. The released ANP circulates to the kidney where it acts through cyclic GMP to produce natriuresis and a return to normal blood volume.

Aspects of neural and hormonal control of water and sodium balance

This article reviews some aspects of neural and hormonal control of water and sodium balance. The maintenance of extracellular fluid volume and osmolarity depends on the coordinated action of multiple mechanisms of water and sodium intake and excretion. Different technics for manipulation of the central nervous system, i.e., withdrawing of nervous structures, electrolytic lesion, electrical stimulation and chemical stimulation, have allowed the identification of some brain areas, neural circuits and neurotransmitters that participate in the mechanisms of control of water and sodium intake and excretion. The signals for thirst and actions of angiotension II, cholinergic agents and atrial natriuretic factor upon drinking are discussed. Three possible types of effector mechanism for centrally induced natriuresis are discussed: 1) renal innervation; 2) secretion of a substance by the brain which causes natriuresis through direct or indirect action (antidiuretic hormone and active sodium transport inhibition); 3) CNS control of the secretion of a hormonal substance produced at another site (mineralocorticoid and atrial natriuretic factor). These mechanisms are not mutually exclusive.

Hypothalamic control of water and salt intake and excretion

This article provides a personal and historical review of research concerning the hypothalamic control of water and salt intake and excretion. The following major points will be considered: 1. Electrical, osmotic, cholinergic, alpha-adrenergic and peptidergic stimulation of the hypothalamus. 2. Determination of the pathways involved in these neuroendocrine responses. 3. The participation of ANP in the control of thirst and salt excretion. 4. The participation of the brain ANPergic neuronal system in ANP release. 5. The role of hypothalamic ANPergic neurons and of sinoaortic and renal baroreceptors in the regulation of volume expansion-induced release of ANP. 6. Effects of the brain ANP system on other hormones.

Angiotensin II antiserum decreases luteinizing hormone-releasing hormone in the median eminence and preoptic aea of the rat

Ovariectomized female rats were sacrificed 3 h after intracerebroventricular microijnjection of normal rabbit serum (NRS), specific antiserum against angiotensin II (AB-AII) or atrial natriuretic factor (AB-ANF). AB-AII decreased plasma LH by 50% and LH-RH content by 70% in the median eminence and medial preoptic area, respectively, but did not change plasma FSH when compared to animals which receivede NRS. There was no difference in these parameters when the animals were injected with AB-ANF or NRS.These results indicate that endogenous AII plays a physiological role in LH release acting directly or indirectly through LH-RH neurons of the median eminence and medial peroptic area

Effect of cholinergic stimulation of the medial septal area on the secretory properties of atrial myocardial fibers

Adult male Wistar rats weighing 240-260 g were implanted with stainless steel guide cannulae into the medial septal area (MSA). Cholinergic stimulation of the MSA increased natriuresis (344.6 + or - 13.8 vs 22.2 + or - 2.1 micronEq for the controls), the number of atrial specific granules (61.0 + or - 6.7 vs 43,8 + or - 3.5 granules/100 micron m**2 sarcoplasma for the controls), and the number of electron-dense vesicles near the sarcolemma or appearing to undergo exocytotic extrusion (50.0 + or - 2.3 vs 21.4 + or - 5.7 vesicles/100 micronm sarcolemma for the controls) It is not yet clear how cholinergic stimulation of the MSA changes the secretory characteristics of atrial myocardial fibers. However, the present study provides evidence that release of an atrial natriuretic factor may be controlled by the central nervous system (CNS). This may occur through the sympathetic and parasympathetic innervation of the heart or through the release of some substance produced by the CNS or produced at another site whose release is controlled by the CNS