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Biomedical subjects

R F Parrott

Publications and source records attributed to R F Parrott.

At least 73 records · Page 4Linked to original sources
PubMed1989

Naloxone affects the release of cortisol, but not of vasopressin or oxytocin, in dehydrated sheep.

Ovariectomized ewes (N = 7) were dehydrated for 24 h and then given iv injections of saline vehicle or 8 or 64 mg naloxone hydrochloride in saline. Blood samples were taken by jugular venepuncture before and after dehydration and at intervals during the 90 min period directly following naloxone treatment. Plasma concentrations of AVP, OT and cortisol were measured by radioimmunoassay. Plasma AVP levels and osmolality increased with dehydration, OT concentrations showed no consistent change, and cortisol levels were unaffected. After administration of naloxone, AVP and OT concentrations did not alter. The sampling procedure increased plasma cortisol levels and the duration of this response was prolonged by the 64 mg dose of naloxone.

Animals↗
PubMed1988

Changes in vasopressin and cortisol secretion during operant drinking in dehydrated pigs.

Two studies were carried out to examine endocrine changes during a 60-min period of operant drinking in 24-h dehydrated pigs. Measurements were made of water intake, osmolality, hematocrit, and plasma concentrations of lysine vasopressin (LVP) and cortisol during rehydration (experiment 1) and of fluid intake, osmolality, and LVP levels during consumption of isotonic saline (experiment 2). Increases in osmolality and LVP produced by dehydration in experiment 1 were rapidly reversed during rehydration with the result that osmolality returned to predeprivation levels after 20 min and LVP after 30 min, but there was no evidence of a decrease in LVP before absorption. Plasma cortisol concentrations were unaffected by dehydration although they declined during the final 40 min of experiment 1. In experiment 2, osmolality remained elevated during saline drinking, but plasma concentrations of LVP declined abruptly. The results suggest that oropharyngeal factors inhibiting vasopressin release, revealed during saline ingestion, are obscured during normal rehydration as a result of the rapid rate at which water is absorbed by the gut in this species.

Animals↗
PubMed1988

Endocrine responses to acute stress in castrated rams: no increase in oxytocin but evidence for an inverse relationship between cortisol and vasopressin.

Plasma concentrations of cortisol, oxytocin, vasopressin and prolactin were measured by radioimmunoassay in eight castrated rams subjected to handling (control), restraint or isolation. Determinations were also made of hematocrit and plasma osmolality. Blood was collected by jugular venipuncture 60 and less than 1 min before, and 5, 15, 30, 60 and 120 min after the start of treatment. Plasma cortisol was raised above pre-treatment levels during isolation and restraint but only transiently after handling. In the first 30 min of treatment, cortisol concentrations were higher following isolation than after restraint or handling and, in the final 60 min, levels were higher during both isolation and restraint than after handling. Oxytocin concentrations showed little change but vasopressin levels were reduced 15, 30 and 60 min after the start of isolation and were negatively correlated with those of cortisol. Plasma prolactin concentrations decreased during handling and restraint but remained unaltered after isolation. Osmolality and hematocrit decreased in all three treatment conditions. These findings indicate that stress does not alter oxytocin levels in sheep, but changes in vasopressin secretion and water balance may occur if cortisol release is greatly enhanced.

Animals↗
PubMed1987

Differential responses of plasma oxytocin and vasopressin to dehydration in non-stressed sheep.

Group housed, castrated rams (N = 10) were studied over a 2 day period. Water was available ad libitum during day 1 (control) but was withheld throughout day 2 (experimental). On both days, blood was collected by jugular venepuncture at 10.30 h, and then again 2, 4, 6 and 24 h later. Plasma samples were analysed by radioimmunoassay for arginine vasopressin (AVP), oxytocin and cortisol content and measurements were also made of the haematocrit and plasma osmolality and electrolyte (Na+, Cl-) concentrations. After 24 h water deprivation there was a significant increase in plasma AVP levels but no changes in oxytocin or cortisol concentrations. Dehydration also significantly depressed the haematocrit and increased plasma osmolality and electrolyte concentrations.

Animals↗
PubMed1987

Endocrine and behavioural factors affecting water balance in sheep subjected to isolation stress.

The effect of stress on drinking, water balance and endocrine profile was studied using ten castrated rams. Individual sheep were exposed to 30-h periods of total isolation (psychological stress) or physical separation from their social group (control). Plasma was analysed for haematocrit, osmolality, electrolyte levels and concentrations of cortisol and arginine vasopressin. Isolation stress significantly reduced water intake, increased haematocrit and plasma concentration of cortisol, but did not alter osmolality or vasopressin concentration. The physiological effects of this self-imposed water restriction contrast with those obtained by depriving the sheep of water for 24 h under conditions that were not stressful, i.e. by keeping them grouped together. These results suggest that cortisol may act to defend plasma volume in sheep exposed to acute stress. The results also indicate that vasopressin probably should not be considered to be a 'stress hormone' in the sheep.

Animals↗
PubMed1986

Minimal effects of 17 beta-hydroxy-17 alpha-methyl-estra-4,9,11-triene-3-one (R1881) on sexual behaviour in prepubertally castrated rams.

Ten adult prepubertally castrated rams were injected with 5 alpha-dihydrotestosterone propionate (DHTP; 20 mg/day) for 3 weeks to stimulate genital development. Thereafter, half of the sheep were injected with testosterone (100 mg/day) for a further 4 weeks, while the remainder received the same dose of 17 beta-hydroxy-17 alpha-methyl-estra-4,9,11-triene-3-one (methyltrienolone; R1881). All the animals were tested for sexual behaviour on 15 occasions with ovariectomized ewes in which oestrous behaviour was induced by injections of 50 micrograms oestradiol-17 beta benzoate at 4- to 5-day intervals. Behavioural tests were of 10 min duration and were carried out thrice weekly over a 5-week period, starting in the final week of DHTP treatment. Animals treated with testosterone showed a highly significant increase in courtship behaviour (tongue-flicks; lunges and nudges) after only four daily injections and this level of activity was maintained to the end of the experiment. However, the incidence of courtship activity in sheep treated with R1881 was similar to that recorded during the period of DHTP treatment. All animals given testosterone displayed mounts with pelvic thrusts and erections, and achieved intromission with ejaculation. These activities remained significantly more frequent than in sheep treated with R1881, starting from tests 9, 8 and 12 respectively. Four of the five individuals in the group given R1881 showed occasional mounts with thrusts, three showed sporadic erections and one sheep intromitted in the final test. These results indicate that, in contrast to the rat, R1881 has only very weak effects on sexual behaviour in the castrated ram.

Animals↗
PubMed1985

Effects of intracerebroventricular injection of naloxone on operant feeding and drinking in pigs.

Operant feeding and drinking to satiation were studied in prepubertal pigs deprived of food or water for 18 hours and then given intracerebroventricular (ICV) injections of a solution of naloxone hydrochloride. In feeding tests there was no difference in the amount of food consumed, or in the rate at which reinforcements were obtained, between pigs given ICV injections of 0.4 or 0.8 mg naloxone and those receiving a control injection of saline. However, in drinking tests, injection of both 0.2 and 0.4 mg naloxone significantly (p less than 0.01) reduced the quantity of water drunk and slowed the rate at which reinforcements were obtained. No significant effects on operant water intake were seen after intravenous injection of 0.4 mg naloxone.

Animals↗
PubMed1984

Sexual and aggessive behaviour of castrated male sheep after injection of gonadal steroids and implantation of androgens in the hypothalamus: A preliminary study.

The combined effects of hypothalamic steroid implants and subcutaneous hormone injections on the courtship, copulatory and aggressive behaviour of five castrated male sheep (wethers) were assessed in thrice weekly tests with sexually receptive ewes. The animals were prepared with bilateral guide tubes for the insertion of removable hormone-containing cannulae aimed at the preoptic/anterior hypothalamic region of the brain. The sheep were treated as follows: weeks 1-4, cholesterol implants + oestradiol dipropionate injections; weeks 5-7, dihydrotestosterone propionate implants + oestradiol dipropionate injections; weeks 10-12, testosterone terone propionate implants + oil injections; weeks 13-15, testosterone propionate implants + dihydrotestosterone propionate injections. During peripheral treatment with oestradiol dipropionate (weeks 1-4), two of five sheep displayed ejaculatory reflexes in the absence of erection and intromission. Moreover, no obvious behavioural effects could be attributed to the additional presence of central dihydrotestosterone propionate implants (weeks 5-7). By contrast, testosterone propionate implants at the same central sites (weeks 10-12) maintained sexual behaviour in four of five sheep, induced mounting in the remaining animal and stimulated aggressive behaviour in all five sheep. Subsequently, additional peripheral treatment with dihydrotestosterone propionate (weeks 13-15) also stimulated three of the animals to exhibit penile erections.

Journal Article↗
PubMed1984

Behavioural and morphological effects of 5 alpha-dihydrotestosterone and oestradiol-17 beta in the prepubertally castrated boar.

Three groups of 5 prepubertally castrated boars received twice weekly subcutaneous injections from 16 to 28 weeks of age of 5 alpha-dihydrotestosterone propionate (1 mg/kg), oestradiol-17 beta dipropionate (0.1 mg/kg), or a combination of the two steroids. The pigs were tested each week for sexual behaviour with an oestrogen-treated ovariectomized gilt. 5 alpha-Dihydrotestosterone did not induce copulatory behaviour whereas oestradiol initiated mounting, although this behaviour was not maintained. However, the combined hormonal treatment induced the full pattern of copulation, including ejaculation, in 4/5 pigs. Oestrogen-treated animals also showed champing and salivation. None of the pigs treated with 5 alpha-dihydrotestosterone showed lordosis when exposed to a mature boar. Increases in the size of the penis, the ischio- and bulbocavernosus muscles, seminal vesicles and bulbourethral glands were produced by 5 alpha-dihydrotestosterone, and, with the exception of the penis, this hypertrophy was further enhanced by additional treatment with oestradiol. Increases in the weight of the prostate and muscular urethra were due mainly to the effects of oestrogen; this steroid caused extensive development of fibromuscular tissue and also increased mammary teat length. In the submaxillary salivary glands, synergism between 5 alpha-dihydrotestosterone and oestradiol resulted in hypertrophy of the serous cells.

Animals↗
PubMed1983

Intravenous cholecystokinin octapeptide in pigs reduces operant responding for food, water, sucrose solution or radiant heat.

The effect of intravenous injections of 0 (Saline vehicle), 10, 20 or 40 units of CCK was studied in pigs performing operant responses for food, water, sucrose solution or radiant heat. In hungry pigs working for food, thirsty pigs responding for water, and non-deprived pigs working for sucrose, 20 and 40 units CCK produced significant dose-related decreases in response rates lasting for about 5 min. In pigs responding for 10 sec bursts of infra-red heat at an ambient temperature of 5 degrees C, 40 units CCK significantly reduced the response rate during the 5 min period following injection.

Animals↗
PubMed1982

Self-stimulation in the sheep: interactions with ingestive behaviour and light cycle.

Self-stimulation was obtained in 5 adult male sheep using a movable electrode system. The effects on response rate of increases in current, food deprivation and satiation were determined. Interactions between feeding, drinking and self-stimulation over longer periods (5 days) were studied in experiments in which individual sheep lived in an isolated continuously illuminated pen. Experimental conditions were as follows:--(1) Food + water available on operant (FR 30); (2) Operant food and water + self-stimulation; (3) Bowl feeding, ad lib water + self-stimulation; (4) As for condition '3' but with 12:12 light/dark cycle. Finally, sheep were tested for stimulation-bound feeding and drinking. The results obtained in these experiments with the sheep, a ruminant, are compared with those previously found for the pig.

Animals↗