Plasma Plasma Prolactin Concentrations Research Articles

Effects of poults on plasma concentrations of prolactin in turkey hens incubating without eggs or a nest.

1. Plasma prolactin (PRL) concentrations, total daylight sitting time and extent of brood patch development were compared in singly caged hens incubating without a nest or eggs and in penned hens incubating eggs in nest boxes. No significant differences were found in any of the three measures of incubation intensity. 2. When 10 newly-hatched poults were placed in the cages of incubating hens their plasma PRL concentrations fell rapidly. No fall in plasma PRL was observed in hens that could see and hear, but not touch the poults. 3. When physical contact between hens and poults was maintained, visual isolation of hens from poults, surgical devocalisation of poults, or the combination of visual isolation and devocalisation of poults had no effect on the poult-stimulated decline in plasma PRL concentrations. 4. Sensory cues from poults that evoke the PRL response in incubating hens are primarily tactile.

Serum and seminal plasma prolactin concentrations in men with normospermia, oligospermia, or azoospermia

Semen analyses were performed and serum and seminal plasma prolactin (PRL) concentrations were determined in 165 samples from 120 men seen with their wives because of infertility. The mean (+/- standard deviation) serum and seminal plasma PRL concentrations were 6.5 +/- 3.3 and 7.5 +/- 3.1 ng/ml, respectively. The mean concentrations of PRL in serum and seminal plasma were similar in groups of men divided by sperm concentration. Seven men had an increased serum PRL concentration. Three of these 7 men had sperm concentrations less than 20 million/ml and none of these 7 men had an increased seminal plasma PRL concentration. Four men had an increased seminal plasma PRL concentration; the serum PRL concentration, sperm concentrations, and motilities were normal in all 4. No man had a decreased serum or seminal plasma PRL concentration. Increased serum PRL concentrations were found infrequently and the increase was slight (23.2 ng/ml or less). Seminal plasma PRL concentrations were related directly to sperm concentrations and motilities, relationships that were statistically significant.

Stressor-associated alterations in porcine plasma prolactin.

Experiments were conducted to determine effects of restraint and thermal stressors on plasma prolactin (PRL) in castrated male pigs. A single 20-min restraining period in a restraining cage which prevented both movement and injury increased (P less than 0.05) plasma PRL when applied at either 0800 or 1600 hr. Exposure to 32 degrees C at 0800-1000 hr or at 1600-1800 hr produced more moderate increases (P less than 0.05). A combination of 20 min restraint and 2 hr at 32 degrees C produced a response similar to restraint alone. Twenty minutes after stressor application plasma PRL concentrations in pigs exposed to restraint or restraint +32 degrees C at 1600 h were greater (P less than 0.05) than concentrations measured in all other treatment groups at that time interval. However, there were no statistically significant differences in additional quantitative indices of the plasma PRL responses (maximal level, maximal change, or integrated response above basal levels) among restraint, 32 degrees C, or restraint +32 degrees C, nor between morning and afternoon applications of treatment. Such data do not provide, therefore, any strong evidence for stressor-dependent or circadian differences in plasma PRL response. A second study subjected castrated male pigs to 20 degrees C (controls), 20 +/- 12 degrees C (cyclic temperature, sine wave variation), 5 degrees C constant, and 5 +/- 12 degrees C cyclic for 20 days. After 6 days exposure to 5 degrees C constant or 5 +/- 12 degrees C cyclic there were decreases (P less than 0.05) of 59 and 67% respectively in plasma PRL when compared either with pretreatment levels or with levels in pigs at 20 or 20 +/- 12 degrees C. There were no differences in PRL responses between cyclic vs constant temperatures. These results are the first to indicate that plasma PRL in pigs is affected by acute restraint and thermal stressors.

Nocturnal plasma prolactin and cortisol levels in epileptics with complex partial seizures and primary generalized seizures.

The nocturnal pattern of plasma prolactin (PRL) and cortisol in male epileptics with complex partial seizures and primary generalized seizures was studied by all-night polygraphic recordings with continuous video monitoring and sequential blood sampling at 30-minute intervals. Mean nocturnal plasma PRL concentrations in both groups of epileptics were significantly elevated when compared with nonepileptic control subjects studied in a similar fashion. Eight subclinical and three clinical partial seizures were recorded during sleep. Although a tenfold increase of plasma PRL level occurred following a short brief clinical complex partial seizure, there was no direct correlation between single subclinical partial seizures and nocturnal fluctuations of plasma PRL concentrations. We did not observe recognizable plasma cortisol changes following partial seizures during sleep, nor significant differences of mean nocturnal plasma cortisol levels between epileptics and controls. The data obtained in this environmentally controlled study indicate that postictal elevation of plasma PRL is a specific phenomenon related to seizure discharges; however, failure of such a rise does not exclude partial seizures.

Effect of catechol estrogens on prolactin secretion in the rat: lack of correlation with estrogenic activity.

Temporal changes in plasma prolactin (PRL) levels caused by the administration of a number of different catechol estrogens to freely-moving conscious male rats were determined. The steroids with a wide range of affinity for the estrogen receptor were given in a single bolus (100 micrograms/kg) into the right atrium via an indwelling cannula. Plasma PRL concentration was monitored by taking blood samples every 2 min. The effect on PRL secretion was found to be more pronounced when the catechol estrogens were administered to rats bearing implants of estradiol and could not be correlated with their Kd values for the estrogen receptor. The synthetic estrogen, diethylstilbestrol, behaved anomalously by producing an elevation in plasma PRL only in estradiol-primed animals or after prolonged infusion. Diethylstilbestrol-treated rats showed no PRL response to 2-hydroxyestrone unlike those bearing Silastic capsules of estradiol. The experiments support the hypothesis that catechol estrogens generally act as short-term dopamine agonists, lowering PRL, but that those which possess estrogenic activity also show a more prolonged PRL-elevating effect. Thus, the overall action of this group of steroids will be determined by factors which influence these two parameters.

Effect of interictal epileptiform discharges on nocturnal plasma prolactin concentrations in epileptic patients with complex partial seizures.

To investigate the effect of interictal epileptiform discharges (IEDs) on plasma prolactin (PRL) level, we studied 18 epileptic patients with complex partial seizures (CPS) who did not experience clinical or subclinical ictal events during all-night monitoring with polygraphic recording and video imaging. The density of IEDs peaked during non-REM stages and was significantly reduced during REM stage. Mean plasma PRL concentrations in epileptic patients, when sampled at 30-min intervals, showed a moderate but significant elevation during non-REM (p less than 0.001) and awake stages (p less than 0.005), but not during REM stage, when compared with 10 nonepileptic control subjects studied in a similar fashion. The data obtained in this physiologically controlled environment indicate that the cumulative effect of IEDs may modify PRL regulatory mechanisms, resulting in a modest elevation of plasma concentrations independent of ictal discharges.

Differential responses in prolactin levels induced by naloxone in humans

The plasma prolactin (PRL) response to the opiate antagonist naloxone was tested in drug-free healthy volunteers (10 men, 18 regularly menstruating women who were in the late follicular phase of their ovarian cycles, and seven post-menopausal women). Naloxone hydrochloride (2 mg intravenous bolus) and placebo (normal saline) were administered on two different days in a double-blind fashion. Blood samples were collected at - 15, 0, 30, 60, 120, 180 and 240 min after the injection. In the women of reproductive age, naloxone reduced plasma PRL concentrations, whereas in the post-menopausal women and the men, naloxone resulted in no significant change. However, in the post-menopausal women treated with estrogen (intramuscular 17-β-estradiol), the opiate antagonist was able to lower plasma PRL concentrations. Thus, it appears that opiate effects on PRL secretion are influenced by the gonadal steroid environment and that estrogens may play a modulating role.

Prolactin and its involvement in fluid regulation in the bovine

1. 1. Plasma prolactin (PRL) concentrations, osmolality, water consumption, feed intake, urine excretion, and fecal water output were determined in twelve steers of 3 breeds exposed to 5 feed and water regimes. 2. 2. Breed differences were found in water intake and plasma PRL concentrations when feed and water were ad lib., however, during any of the other 4 treatments, responses were similar between breeds. 3. 3. During dehydration and feed restriction, water intake, urine, fecal water, and plasma prolactin decreased; however, during hydration and refeeding such changes were not as clearly related. 4. 4. No consistent relationships between plasma prolactin and osmolality were found. 5. 5. Data suggests that PRL's role in fluid regulation in the bovine is most likely associated with alterations in renal hemodynamics rather than by changes in plasma osmolality.

NEUROENDOCRINE ASPECTS OF CENTRALLY ACTING HYPOTENSIVE DRUGS

1 The effects of chronic treatment with methyldopa on plasma prolactin (PRL) levels and of the acute administration of guanfacine on growth hormone (GH) release in acromegalic patients were investigated. 2 Elevated plasma PRL concentrations were observed in five of eight patients during chronic treatment with methyldopa (750 mg/day) for 3–8 months. Three male patients complained of loss of libido and/or impotence. Addition of bromocriptine (7.5 mg/day) to methyldopa therapy normalized the PRL levels and sexual function, while it resulted in a further decrease in blood pressure. 3 Guanfacine as an acute test dose is a strong stimulator of GH secretion. We investigated the effect of guanfacine (2 mg orally) on plasma GH levels in six acromegalic patients. In five patients, the elevated plasma GH levels showed a paradoxical decrease from 90 to 180 min after the administration of the drug, while blood pressure remained unchanged. 4 Guanfacine appears to be a safe drug in patients with GH-secreting pituitary tumours and may possibly be beneficial.

A preliminary study of sex-related differences in prolactin responses to dopamine blockade and insulin hypoglycemia and in penfluridol plasma levels in schizophrenic patients.

Twelve healthy chronic schizophrenic patients were treated with the long-acting oral dopamine (DA) receptor blocker penfluridol (100 mg orally) for 6 weeks. Plasma prolactin (PRL) levels were measured during insulin-tolerance tests (ITT) performed at the end of the drug-free period (7-10 days) and during weeks 1 and 6 of penfluridol treatment. Simultaneous PRL and penfluridol plasma levels were determined just prior to, and at 8, 72 and 120 h after penfluridol administration during weeks 1, 5, and 6. During penfluridol treatment women (N = 4) had a greater increase in their maximal PRL increments after ITT as compared to the men (N = 8). Analyses of (peak) plasma penfluridol and PRL concentrations 8 h after penfluridol administration revealed a trend towards lower plasma penfluridol levels during weeks 5 and 6 and significantly higher PRL levels in women compared to men during weeks 1 (P less than 0.01), 5 (P less than 0.02), and 6 (P less than 0.02). The consistent sex-related differences in the PRL responses to DA blockade, and to insulin-induced hypoglycemia and in the penfluridol plasma levels in our study support the view that sex-related changes need to be considered not only in the hormonal responses to various pharmacological agents, but also in the assessment of the plasma levels of these drugs.

Inhibition of naloxone of prolactin release induced by L-5-hydroxytryptophan in rats.

AbstractIntravenous injection of l-5-hydroxytryptophan (l-5-HTP), but not l-5-HTP, resulted in an increase in plasma prolactin (PRL) levels in anesthetized rats. l-5-HTP-induced PRL release was blunted by naloxone, a specific opiate antagonist. In rats pretreated with either reserpine or α-methyl-p-tyrosine (α-MT), basal plasma PRL levels were elevated and l-5-HTP injection caused a further increase in plasma PRL concentrations. However, PRL release induced by l-5-HTP was not blunted by naloxone in these animals pretreated with reserpine and α-MT. These results suggest that PRL release induced by serotonin is modulated, at least in part, by opioid peptidergic mechanisms, which are closely related to brain catecholamines.

Nursing-Mediated Prolactin and Luteinizing Hormone Secretion During Puerperal Lactation

Alterations in plasma prolactin (PRL) concentrations in response to nursing in puerperally lactating women are often significant beyond the 90th postpartum day, yet the increment appears unrelated to the frequency or duration of the nursing stimulus. Tonic gonadotropin secretion is low, assuming a more episodic secretory pattern either when the frequency of breast-feeding is reduced or when weaning takes place. Significant increments in peripheral concentrations of luteinizing hormone can be seen in response to weaning coincident with a fall in peripheral plasma PRL concentration. At the same time, peripheral estrogen concentrations increase, suggesting that a specific set point for ovarian responsiveness to gonadotropins exists. Whether this set point is related solely to the peripheral concentration of gonadotropins or whether it is also related to the peripheral PRL concentration is not known at this time.

Plasma prolactin in undisturbed cannulated male rats; effects of perphenazine, frequent sampling, stress and castration plus oestrone treatment.

ABSTRACT Blood was collected from undisturbed male rats by means of chronically indwelling intrajugular cannulae and the plasma prolactin (PRL) concentration was determined by a radioimmunoassay. The effect of perphenazine, frequent bleeding, handling and brief ether stress in normal males and of stress in castrated oestrone treated males was determined. The plasma PRL concentration in undisturbed intact males was low. Castration plus oestrone treatment for 3 or 7 weeks had little or no effect on the PRL concentration. Neither frequent blood sampling nor removal of 3 ml blood over a period of 5 h affected plasma PRL concentration. Intravenous administration of perphenazine caused a striking and prolonged increase in plasma PRL in intact males. Brief handling or mild ether stress caused a significant rise in PRL within 2 min in intact males; 15–20 min later PRL had returned to the undisturbed level. Brief ether stress in oestrone treated castrates induced a comparable pattern of prolactin release, although of greater magnitude. In these animals a second stress one hour later induced a similar response. It is concluded that chronic cannulation neither affects the unstressed prolactin level nor interferes with the ability of the adenohypophysis to release PRL. The results also indicate that when rats are handled a truly stress free sample can only be obtained when the blood is drawn within one minute after the initial disturbance of the animal. The evidence presented indicates that oestrone treatment increases the responsiveness of male rats to stress-induced PRL release.