Biomedical subjects

D R Grattan

Publications and source records attributed to D R Grattan.

43 records · Page 3Linked to original sources

PubMed1993

Differential effects of adrenalectomy on the prolactin-induced suppression of LH and FSH secretion after castration in male rats.

Hyperprolactinaemia inhibits gonadotrophin secretion in males and females of many species. The aim of this study was to determine the role of the adrenal gland in mediating the inhibitory effects of prolactin by contrasting the effects of acute hyperprolactinaemia on LH and FSH secretion in adrenal-intact and adrenalectomized rats with and without physiological corticosterone replacement. Adult male rats were administered purified ovine prolactin every 12 h (2.4 mg per injection s.c.) beginning at the time of castration. Blood samples were collected every 3 h for 36 h, then every 12 h until 10 days after castration. Ovine prolactin significantly reduced LH secretion in all groups from approximately 15 to 48 h after castration. In contrast, plasma FSH concentrations were reduced by ovine prolactin from 21 to 48 h only in the adrenal-intact rats and not in the adrenalectomized or adrenalectomized plus corticosterone groups. In all groups, ovine prolactin inhibited endogenous prolactin secretion in rats by short-loop autofeedback as soon as 3 h after the first ovine prolactin injection and throughout the 10 days of the study. Adrenalectomy per se, with or without corticosterone replacement, also had a differential effect on LH and FSH secretion after castration, causing only a transient delay in the rise in LH after castration, but inducing a significant and long-lasting inhibition of FSH secretion. The results demonstrate that ovine prolactin-induced suppression of LH secretion after castration occurs with or without the adrenal glands. Suppression of FSH secretion after castration by ovine prolactin, however, may involve an adrenal component.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Glands↗

PubMed1993

Effect of alcohol, neurohypophysectomy, and vasopressin antagonists on hemorrhage-induced bradycardia in the rat.

During initial stages of hemorrhage in the rat, cardiovascular compensation leads to a tachycardia (mean +/- SE, 5.2 +/- 0.7%; n = 23) that helps prevent a large fall in blood pressure. This compensatory phase is followed by a decompensatory phase in which mean arterial pressure and heart rate fall. A rise in arginine vasopressin (AVP) levels has been postulated as the cause of this hemorrhage-induced bradycardia (HIB). The object of the present study was to determine whether interference with AVP release by alcohol anesthesia or neurohypophysectomy or by blockade of AVP receptors in the plasma or cerebral spinal fluid could attenuate HIB. Male Wistar rats were anesthetized with pentobarbital, surgically prepared, and bled to maintain a blood pressure of 40-50 mm Hg. After hemorrhage, heart rate decreased 15 +/- 2% (n = 6) with alcohol anesthesia compared with 32 +/- 3% (n = 7) with pentobarbital. After neurohypophysectomy, however, HIB remained unchanged (-15 +/- 2%; n = 5) compared with sham-operated controls (-19 +/- 3%; n = 6). Peripheral administration of two nonselective V1/V2 antagonists and one V2 antagonist had no effect on HIB, whereas a V1 antagonist significantly attenuated the heart rate decrease (-15 +/- 4%; n = 6) compared with controls (-32 +/- 3%; n = 7). None of the AVP antagonists tested at one tenth the peripheral dose had any effect on HIB when administered into the lateral ventricle of the brain, although a mixed serotonin, dopamine, and catecholamine antagonist, spiperone, potentiated the response. It was concluded that although peripheral release of AVP may be partially involved in the heart rate response to hemorrhage, central AVP release and central AVP receptors were not involved in HIB.

Animals↗

PubMed1991

Posterior pituitary lobectomy chronically attenuates the nocturnal surge of prolactin in early pregnancy.

The posterior pituitary gland contains a potent PRL-releasing factor (PRF). The aim of this study was to determine whether this PRF was involved in the luteotropic PRL surges of early pregnancy. The posterior pituitary was removed from a group of rats at least 4 weeks before the experiment (LOBEX). LOBEX rats were tested for diabetes insipidus and checked postmortem for the absence of posterior lobes. Plasma samples were taken from these chronically LOBEX rats as well as from sham-operated and unoperated controls beginning at noon on day 3 of pregnancy and continuing for 3 days at times most likely to demonstrate the twice daily surges of PRL secretion. PRL in all groups was basal (less than 12 ng/ml) at noon and rose to a diurnal peak at 1800 h. While the unoperated and sham-operated controls then displayed a clear nocturnal surge of PRL, peaking at 300-400 ng/ml at 0300 h, LOBEX rats had a significantly attenuated peak of 102.7 +/- 17.7 ng/ml (P less than 0.001). On subsequent nights the nocturnal peaks were similarly attenuated in LOBEX rats, averaging 80.3 and 42.1 ng/ml on days 5 and 6, respectively. LOBEX rats all had normal sized litters, but lactation yields were depressed. These data support the hypothesis that the posterior pituitary secretes a potent PRL-releasing factor because its removal partially blocked the mating-induced nocturnal surge of PRL.

Animals↗

PubMed1991

Role of the placenta in the control of the ante-partum surge of prolactin in the rat.

A nocturnal surge of prolactin secretion occurs in the dark period preceding parturition in the rat. The aim of this study was to examine the role of the placenta in the control of this prolactin surge. Plasma prolactin and progesterone were measured by radioimmunoassay in serial blood samples collected after surgical removal of conceptuses during late pregnancy, and after intracerebroventricular (i.c.v.) injection of placental lactogen (PL) before the prolactin surge. In intact control animals, prolactin secretion remained low until a nocturnal surge of secretion occurred in the dark period preceding parturition, peaking at 269 +/- 51 (S.E.M.) micrograms/l at 03.00 h on day 21. Progesterone levels fell from greater than 200 nmol/l on day 19 to less than 40 nmol/l by 12.00 h on day 20 of pregnancy. PL levels during late pregnancy were modified by partial or complete removal of conceptuses at 10.00 h on day 19 of pregnancy. Removal of all but one or two conceptuses did not change the normal pattern of prolactin or progesterone secretion. Removal of all conceptuses, however, induced a large nocturnal surge of prolactin secretion, peaking at 211.7 +/- 78 micrograms/l at 03.00 h on day 20, 24 h earlier than the surge in intact animals. Progesterone levels after removal of all conceptuses fell to less than 40 nmol/l by 23.00 h on day 19, approximately 12 h before the decline in intact animals. Maintenance of increased progesterone levels after conceptus removal using silicone tubing implants significantly (P less than 0.05) reduced the peak of the premature prolactin surge to 79.7 +/- 18 micrograms/l at 05.00 h on day 20.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Intrahypothalamic pituitary grafts elevate prolactin in the cerebrospinal fluid and attenuate prolactin release following ether stress.

Anterior pituitary (AP) tissue grafted into the hypothalamus of female rats inhibits the luteotrophic prolactin (PRL) secretion which normally follows mating. Dopamine blockade has been shown to overcome this inhibition, suggesting that the grafts suppress PRL release from the in situ pituitary by the action of graft PRL increasing dopamine activity in the hypothalamus. To examine whether PRL levels in the cerebrospinal fluid (CSF) were elevated by the AP grafts, CSF samples were taken from 5 control rats and 10 rats bearing intrahypothalamic AP grafts. Mean PRL concentrations in the CSF of the control rats were 3.0 +/- 0.8 ng/ml. The grafted rats had significantly higher concentrations of PRL in their CSF, averaging 23.2 +/- 4.2 ng/ml (P less than 0.005). Plasma PRL concentrations were similar in the control and grafted rats. PRL release in response to 5 min of ether stress was examined in 8 control and 11 grafted rats. In control animals, PRL rose from 4.2 +/- 1.5 to 44.7 +/- 9.0 ng/ml following exposure to ether, but the response was significantly attenuated in the grafted rats, peaking at 9.3 +/- 1.4 ng/ml (P less than 0.001). This inhibition of response due to the grafts was evident within 1 week of graft placement. The results confirm that the presence of intrahypothalamic AP grafts led to the accumulation of supranormal PRL concentrations in the CSF. This elevated PRL suppressed pituitary PRL release in response to ether stress, probably by an autoregulatory feedback activation of the inhibitory tuberoinfundibular dopaminergic neurons in the hypothalamus.

Animals↗

PubMed1990

Effect of ovarian steroids on a nocturnal surge of prolactin secretion that precedes parturition in the rat.

PRL secretion in several physiological and experimental conditions, including early pregnancy, is linked to the daily photoperiod. The aim of this study was to examine the antepartum increase in PRL secretion for evidence of a circadian pattern of release, as seen during early pregnancy. During the last 3 days of pregnancy blood samples were taken six times daily by means of previously implanted jugular cannulae. Plasma PRL concentrations were then measured by RIA. PRL levels were less than 10 ng/ml in all animals on day 19 of pregnancy, but during the light period of day 20 there was an increase to an average of 30 +/- 10 ng/ml, with no evidence of a peak related to the time of day. However, in the dark period between days 20 and 21 there was a large surge of PRL secretion which reached peak levels of 356 +/- 39 ng/ml at 0500 h on day 21, then returned to 48 +/- 20 ng/ml at 1200 h, around the time of parturition. The peak always occurred at 0500 h and was not related to the time of parturition which ranged from 1000-2200 h on day 21. Bilateral ovariectomy (OVX) on day 19 advanced the time of delivery by approximately 12 h. In seven of nine animals, no surge of PRL secretion was observed during the dark period preceding parturition. Estradiol treatment after OVX on day 19 (OVX+E) advanced the time of delivery by approx 18 h. An antepartum PRL surge was present and was advanced by 24 h in all OVX+E animals, peaking at 0300 h on day 20. Progesterone treatment from day 18 to 21 in intact pregnant animals delayed parturition by approximately 18 h and prevented PRL secretion during the period of treatment. After progesterone treatment was stopped, a nocturnal surge of PRL secretion occurred, peaking at 0500 h on day 22, 24 h after the surge in normal animals. The results suggest that the increased PRL secretion during late pregnancy is linked to the daily photoperiod and is characterized by a nocturnal surge in the dark period preceding parturition. This surge is inhibited by progesterone, and it can be advanced 24 h by estradiol treatment in the absence of the ovaries.

Animals↗

PubMed1989

Failure of an indirect competitive enzyme-linked immunosorbent assay to measure prolactin in rat plasma samples.

An indirect competitive enzyme-linked immunosorbent assay (ELISA) for rat prolactin was applied to the measurement of prolactin (PRL) in plasma. The assay involved PRL adsorbed to a 96-well plate competing with soluble PRL in the sample for rabbit anti-rat PRL antibody-binding sites. Antibody bound by the PRL on the well was detected by a goat anti-rabbit immunoglobulin antibody conjugated to the enzyme horseradish peroxidase. Dilutions of PRL in plasma-free assay buffer produced accurate and reliable standard curves over a range of 1-500 ng/ml. Plasma or serum samples, however, gave very low absorbance values, suggesting falsely high levels of PRL in the samples. For example, hypophysectomized rat plasma and fetal calf serum gave readings equivalent to over 250 ng/ml rat PRL by ELISA, whereas radioimmunoassay confirmed the expected PRL values of less than 5 ng/ml. This result indicated considerable nonspecific interference by the plasma. Inclusion of 20% or 50% hypophysectomized rat plasma in the assay significantly lowered the absorbance values and the slope of the standard curve (P less than 0.05). Dilution of plasma samples 1:1 and 1:4 with assay buffer caused nonlinear changes in absorbance and resulted in inaccurate ELISA estimates of plasma PRL concentrations compared with radioimmunoassay. Several treatments were attempted to remove the interference from plasma. Preexposure of plasma to 56 degrees C for 30 min, dialysis for 24 hr, fractional precipitation with 5% polyethylene glycol, increased ionic strength of the buffer, preadsorption of plasma with rabbit immunoglobulins bound to a solid phase support, and covalent attachment of the PRL to the wells with 2% glutaraldehyde all failed to remove the interference from the plasma samples in the ELISA. Thus, while the assay worked effectively for plasma-free applications, it was unsuitable for measurement of PRL in plasma or serum samples.

Animals↗