Effects of pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP) on prolactin, luteinizing hormone and growth hormone secretion in the ewe

This study was undertaken to investigate the roles of PACAP and VIP in the control of pituitary hormone secretion in the ewe. The first experiment was designed to identify any direct effects at the level of the pituitary and was conducted during the luteal phase of a prostaglandin-synchronized oestrous cycle. PACAP (0.008, 0.04, 0.2 and 1.0 nmol/min) or VIP (0.06, 0.2, 0.6 and 1.8 nmol/min) was infused into the carotid artery over a 10 min period. Blood samples were taken before and after the infusions so that plasma PRL, LH and GH concentrations could be measured. Blood pressure was also monitored to determine if the doses used were biologically active. In no case was an effect on hormone secretion observed. In contrast, the highest dose of each peptide induced an increase in heart rate to almost three-fold the resting value. Although both peptides are active in vivo, this result suggests that neither peptide has a direct effect on hormone release from the pituitary of prostaglandin-synchronized ewes. In a second experiment, we investigated whether the peptides had central effects on hormone secretion. Intracerebroventricular (ICV) injection of PACAP or VIP at the dose 10 nmol was tested in ovariectomized ewes. After injection, PACAP suppressed PRL and GH secretion so that plasma hormone concentrations from 1-3 h after injection were significantly different from the control (P < 0.05 for PRL, P < 0.01 for GH). In addition, PACAP significantly reduced mean LH concentration (P < 0.05) and LH pulse frequency (P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS

A method for drug infusion into the lateral median eminence and arcuate nucleus of sheep

The role of catecholamines in the control of the GnRH pulse generator is unclear as studies have relied on the use of peripheral or intracerebroventricular injections, which lack specificity in relation to the anatomical site of action. Direct brain site infusions have been used, however, these are limited by the ability to accurately target small brain regions. One such area of interest in the control of GnRH is the median eminence and arcuate nucleus within the medial basal hypothalamus. Here we describe a method of stereotaxically targeting this area in a large animal (sheep) and an infusion system to deliver drugs into unrestrained conscious animals. To test our technique we infused the dopamine agonist, quinpirole or vehicle into the medial basal hypothalamus of ovariectomised ewes. Quinpirole significantly suppressed LH pulsatility only in animals with injectors located close to the lateral median eminence. This in vivo result supports the hypothesis that dopamine inhibits GnRH secretion by presynaptic inhibition in the lateral median eminence. Also infusion of quinpirole into the medial basal hypothalamus suppressed prolactin secretion providing in vivo evidence that is consistent with the hypothesis that there are stimulatory autoreceptors on tubero-infundibular dopamine neurons. (C) 1997 Elsevier Science B.V

Effects of pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP) on hormone secretion from sheep pituitary cells in vitro

Although vasoactive intestinal polypeptide (VIP) is thought to be a prolactin releasing factor, in vivo studies on sheep suggest that it is inactive in this species. Recent studies, based primarily on the rat, suggest that the related pituitary adenylate cyclase-activating polypeptide (PACAP) is also a hypophysiotrophic factor but again in sheep, this peptide has no in vivo effects on hormone secretion despite being a potent activator of adenylate cyclase in vitro. This lack of response to either peptide in vivo in sheep could be due to the low concentration of peptide that reaches the pituitary gland following peripheral injection. In the present study we therefore adopted an alternative approach of evaluating in vitro effects of these peptides on GH, FSH, LH or prolactin secretion from dispersed sheep pituitary cells. In a time-course study, PACAP (1 mu mol/l) increased GH concentrations in the culture medium between 1 and 4 h and again at 12 h but had no effect in the 6 and 24 h incubations. Prolactin, LH and FSH were not affected by PACAP. The response to various concentrations of PACAP (1 nmol/l-1 mu mol/l) were then evaluated using a 3 h incubation. Again prolactin and LH were not affected by PACAP and there was a small increase in GH concentrations but only at high concentrations of PACAP (0.1 and 1 mu mol/l; P&lt;0.05), PACAP also stimulated FSH secretion in cells from some animals although this effect was small, The GH response to PACAP was inhibited by PACAP(6-38), a putative PACAP antagonist; but not by (N-Ac-Tyr(1), D-Arg(2))-GHRH(1-29)-NH2, a GH-releasing hormone (GHRH) antagonist. The cAMP antagonist Rp-cAMPS was unable to block the GH response to PACAP suggesting that cAMP does not mediate the secretory response to this peptide. At incubation times from 1-24 h, VIP (1 mu mol/l) had no effects on prolactin, LH or GH secretion and, in a further experiment based on a 3 h incubation, concentrations of VIP from 1 nmol/l-1 mu mol/l were again without effect on prolactin concentrations. Interactions between PACAP and gonadotrophin releasing hormone (GnRH), GHRH and dopamine were also investigated. PACAP (1 nmol/l-1 mu mol/l) did not affect the gonadotrophin or prolactin responses to GnRH or dopamine respectively. However, at a high concentration (1 mu mol/l), PACAP inhibited the GH response to GHRH. In summary, these results show that PACAP causes a modest increase in FSH and GH secretion from sheep pituitary cells but only at concentrations of PACAP that are unlikely to be in the physiological range. The present study confirms that VIP is not a prolactin releasing factor in sheep

Effects of pituitary adenylate cyclase activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP) on the cardiovascular system in sheep

The cardiovascular effects of PACAP and VIP were studied in intact conscious sheep; PACAP (0.008, 0.04, 0.2, and 1.0 nmol/min) and VIP (0.07, 0.2, 0.6, and 1.8 nmol/min) were infused in conscious sheep for periods of 10 min. For each peptide there was a dose-dependent increase in heart rate. At the highest doses tested, pulse pressure and mean arterial pressure tended to increase and decrease, respectively. However, only the decrease in mean arterial pressure following the highest dose of VIP reached significance. At the highest doses tested, heart rate increased nearly threefold during the infusion while mean arterial pressure declined by 18.5%. In individual animals the decrease in blood pressure and increase in heart rate occurred simultaneously, so that we were unable to conclude whether the increase in heart rate was due to a baroreceptor reflex

Expression of pituitary adenylate cyclase activating polypeptide type 1 receptor (PAC1R) in the ewe hypothalamus: Distribution and colocalization with tyrosine hydroxylase-immunoreactive neurones

We have examined the distribution of the pituitary adenylate cyclase activating polypeptide type I receptor (PAC1R) in the ewe hypothalamus by reverse transcription-polymerase chain reaction, in situ hybridization and immunohistochemistry. PAC1R mRNA was highly expressed in the mediobasal hypothalamus of the ewe, particularly in the arcuate nucleus and ventromedial hypothalamus, compared to other hypothalamic regions. Similar results were obtained from immunohistochemistry using a specific PAC1R antibody. Intense immunolabelling was observed in the arcuate nucleus, external zone of the median eminence and ventromedial hypothalamus. Only relatively weak immunolabelling was observed in other hypothalamic regions, including the paraventricular nucleus and supraoptic nucleus. In the ewe, PACAP acts via the arcuate nucleus to suppress prolactin secretion. Therefore we examined whether PAC1R was present on the tuberoinfundibular dopamine (TIDA) neurones in this nucleus. Dual immunofluorescence labelling for PAC1R and tyrosine hydroxylase revealed that 21.2 ± 1.7% of dopaminergic neurones in the arcuate nucleus (A12 cell group) also stained for PAC1R. By contrast, other hypothalamic dopaminergic cell groups (A11, A13, A14 and A15) exhibited little (< 3%) or no colocalization. Overall, our results indicate that, in the ewe hypothalamus, PAC1R is most concentrated in the arcuate nucleus, where it is localized on a substantial proportion of dopaminergic neurones. These observations, together with previous in vivo studies, suggest that PACAP could act directly on TIDA neurones via PAC1R to increase dopamine release and consequently inhibit prolactin secretion in the sheep

DNA barcoding relates Trichuris species from a human and a man’s best friend to non-human primate sources

Trichuris trichiura, the whipworm of humans, is one of the most prevalent soil-transmitted helminths (STH) reported worldwide. According to a recent study, out of 289 STH studies in Southeast Asia, only three studies used molecular methods. Hence, the genetic assemblages of Trichuris in Southeast Asia are poorly understood. In this study, we used partial mitochondrial DNA (cytochrome c oxidase subunit 1 or COI) sequences for analysis. Trichuris grouped in a same clade with different hosts indicate the potential of cross infection between hosts. Based on COI, the adult Trichuris isolated from a Malaysian patient was most closely related to Trichuris isolated from Papio anubis (olive baboons) from the USA. The Trichuris isolated from the dog from Malaysia was genetically similar to a Trichuris species isolated from Macaca silenus (lion-tailed macaque) from Czech Republic. Both the human and dog isolated Trichuris grouped in clades with different hosts indicating the potential of cross infection between hosts. Specific PCR primers based on the partial COI of T. trichiura isolated from African green monkey and T. serrata were designed and successfully amplified using multiplex PCR of the pooled DNA samples. Our results suggest a complex parasite-host relationship, and support the theory of cross infection of Trichuris between humans and non-human primates as suggested in previous publications

Comparison of plants used for skin and stomach problems in Trinidad and Tobago with Asian ethnomedicine

RefereedThis paper provides a preliminary evaluation of fifty-eight ethnomedicinal plants used in Trinidad and Tobago for skin problems, stomach problems, pain and internal parasites for safety and possible efficacy. Thirty respondents, ten of whom were male were interviewed from September 1996 to September 2000 on medicinal plant use for health problems. The respondents were obtained by snowball sampling, and were found in thirteen different sites, 12 in Trinidad and one in Tobago. The uses are compared to those current in Asia. Bambusa vulgaris, Bidens alba, Jatropha curcas, Neurolaena lobata, Peperomia rotundifolia and Phyllanthus urinaria are possibly efficacous for stomach problems, pain and internal parasites. Further scientific study of these plants is warranted