PubMed Health⌕ Search

Biomedical subjects

J Terkel

Publications and source records attributed to J Terkel.

At least 55 records · Page 3Linked to original sources
PubMed1983

Failure of rat placenta to inhibit prolactin secretion by ectopic pituitary gland.

At mid-pregnancy in the rat, episodic secretion of pituitary prolactin ceases when the placenta is sufficiently developed. At this time, sufficient placental lactogen is secreted by the placenta to inhibit prolactin secretion. The present study tested whether the fully developed placenta at mid-pregnancy can inhibit prolactin secreted by a donor pituitary gland implanted under the kidney capsule. Three pituitary glands were implanted in rats on day 7 of pregnancy; muscle fragments were implanted in controls. Blood was collected during the first and second halves of pregnancy. It was found that prolactin concentrations in the animals with the pituitary implants were high on days 9 and 10 of pregnancy and remained raised during the second half of pregnancy while in control animals nocturnal surges were absent in the second half of pregnancy, the last one occurring on day 10. This observation indicates that the placental hormone cannot act directly on the pituitary gland to inhibit prolactin secretion, but presumably exerts its suppressive effect on prolactin secretion through the hypothalamus.

Animals↗
PubMed1983

Thyroid stimulating hormone and prolactin secretion: reduced sensitivity to TRH-stimulated prolactin release after midpregnancy in rats.

Prolactin (PRL) and thyroid stimulating hormone (TSH) plasma concentrations were measured during the latter part of the dark period in early and mid-late pregnancy in the rat. On Days 4-5 and 7-8 of pregnancy, plasma PRL concentrations surged between 22:00 and 06:00 hr and TSH values increased between 22:00 and 02:00 hr. While the TSH pattern was maintained during the second-half of pregnancy, surges in PRL release ceased and PRL levels remained at less than 10 ng/ml. The effects of thyrotropin releasing hormone (TRH) administration on PRL and TSH secretion were then measured to determine whether the second-half of pregnancy is associated with a decrease in sensitivity to an agent that can stimulate PRL release. Injection (iv) of cannulated pregnant rats with a low dosage (20 ng) of TRH stimulated a twofold increase in plasma TSH during both early (Days 5-9) and later (Days 14-18) pregnancy but did not change plasma PRL levels. Treatment with a high dosage (2 micrograms) of TRH induced a sixfold rise in plasma TSH during both phases of gestation. The higher dose of TRH also stimulated elevations in plasma PRL during early and mid-late pregnancy; however, both the absolute increase in the amount of PRL in plasma and the percentage increase over baseline levels were greater from Days 5-9 than from Days 14-16 of gestation. These data indicate that the neuroendocrine sensitivity to factors that stimulate PRL secretion changes as pregnancy progresses, and suggest that nocturnal secretion of PRL and TSH during pregnancy may be regulated, in part, by a common trophic factor.

Animals↗
PubMed1982

Endogenous inhibition of prolactin secretion in pregnant lactating rats.

The purpose of the present study was to test whether rat placental lactogen, proposed to be inhibitory for endogenous rhythmic PRL secretion during pregnancy, is also inhibitory for a neurally mediated PRL response to exogenous stimulation, i.e. suckling. Pregnant lactating rats were used as the model in this study. Blood samples for PRL were taken via a chronic atrial cannula before and after 30 min of suckling stimulation in the following groups of females: 1) bearing conceptuses of different degrees of development; 2) after removal of conceptuses; and 3) after injection of placental extract immediately before exposure to suckling stimulation. It was found that 1) the PRL response to suckling diminished in conjunction with placental development and the known concomitant rise in rat placental lactogen; 2) removal of the conceptuses permits elevation of PRL after suckling stimulation; and 3) injection of placental extract obtained on days 11-12 of pregnancy failed to block the elevation of PRL in response to suckling. It was concluded that 1) lactation can be maintained even in the presence of very low levels of PRL, provided developed placentae are present, and 2) the developed placentae are capable of inhibiting the acute PRL release in response to exogenous stimulation as well as endogenous rhythmic PRL secretion.

Animals↗
PubMed1982

Absence of nocturnal autonomic prolactin secretion during lactation in the rat.

During pseudopregnancy in the rat prolactin is secreted autonomously in a characteristic pattern of two daily surges, one nocturnal and one diurnal. The present study investigated whether, during lactation, prolactin secretion occurred in an autonomous nightly surge pattern, in addition to secretion resulting from suckling stimulation. Nocturnal levels of prolactin were measured daily for 2 weeks in lactating rats which were separated from their young from 21.00 to 06.00 h. It was found that no nocturnal prolactin surges were present throughout the 2 weeks of lactation. In addition, it was observed that after pups were removed for 3 h prolactin levels were lower during the first week of lactation than during the second week. It was concluded that lactational dioestrus is distinguished from pseudopregnancy by the absence of autonomous secretion of prolactin in the pattern of a nocturnal surge.

Animals↗
PubMed1980

Effects of small medial preoptic area lesions on maternal behavior: retrieving and nest building in the rat.

Previous studies in rats have demonstrated that large lesions in the medial preoptic area (MPOA) disrupt all aspects of maternal behavior. In the present study, small bilateral electrolyte lesions in the MPOA of lactating females abolished nest building and retrieving components of maternal behavior while crouching and nursing were unaffected. Animals which failed to show retrieval and nest building behaviors tended to have a greater area of lesion within the more dorsal part of the MPOA. Although the dorsal MPOA may play a role in the maintenance of the active components of maternal behavior, i.e. nest building and retrieving, another critical factor in determining which components of maternal behavior are disrupted may be the size of the lesion. As one increases the area of damaged tissue there is also an accompanying increase in the components of maternal behavior which are disrupted. No correlation was found between damage to the Sexually Dimorphic Nucleus of the preoptic area and retrieving and nest building.

Animals↗
PubMed1980

Induction by young of prolonged dioestrus in virgin rats behaving maternally.

The present investigation examined, by study of daily vaginal smears, whether the interaction of virgin female rats with young affected the oestrous cycle. Virgins behaving non-maternally or maternally were continuously exposed to young for extended periods. (1) All non-maternal virgins continued to cycle while 87% of maternal virgins ceased to cycle when exposed to young, and entered a series of prolonged dioestrous phases, each lasting about 14 days. Likewise, all maternal parous non-lactating controls exposed to young entered prolonged dioestrus. (2) The dioestrous phase induced by young in virgins was characterized by the decidual response. (3) Young aged 4-9 days were as effective as 10-15-day-old young for inducing and maintaining the dioestrus. (4) Confinement of young in a wire-mesh basket showed that body contact with young was essential to establish dioestrus. (5) Body contact with young was sufficient to induce dioestrus in maternal virgins with excised nipples. (6) Once established, the dioestrus could be maintained for about 12 days after removal of young as early as Day 4 of dioestrus in virgin and parous non-lactating females, but removal of young on Day 6 from post-partum lactating females resulted in a rapid resumption of cyclicity. (7) Prolonged suckling during a series of dioestrous phases induced lactation in 61% of maternal virgins, as well as in all parous control females.

Age Factors↗
PubMed1980

Timing of termination of nocturnal prolactin surges in pregnant rats as determined by the number of fetuses.

In female rats bearing an average litter of 10+/-0.28 fetuses, pituitary prolactin is secreted in a pattern of two daily surges during the first 10 days of pregnancy only. When the number of fetuses was experimentally reduced, prolactin surges continued for a longer period and pregnancy was correspondingly lengthened. The relationship found between a reduced number of fetuses, and delay in termination of prolactin surges further supports the view that, during pregnancy, rat placental lactogen exerts a major influence in inhibiting secretion of prolactin by the maternal pituitary gland. The constant relationship found in all groups between termination of nocturnal surges of prolactin and parturition indicates that it is the interval between implantation and termination of prolactin surges which is prolonged in female rats with small litters.

Animals↗
PubMed1980

Daily rhythm in secretion of prolactin in androgenized female rats.

Androgen-sterilized female rats were obtained by administering 10 micrograms testosterone propionate to pups on day 2 after birth. In contrast with ovariectomized adults, androgenized adult female rats are incapable of responding to cervical stimulation by secreting prolactin in the nocturnal surge pattern. In spite of the loss of this pattern the androgenized female rats still exhibited a daily circadian rhythm of prolactin secretion with afternoon levels three times higher than those after midnight.

Animals↗
PubMed1979

Effects of transecting lateral neural connections of the medial preoptic area on maternal behavior in the rat: nest building, pup retrieval and prolactin secretion.

In lactating female rats bilateral parasagittal cuts transecting the dorsolateral neural connections of the medial preoptic area (MPOA) abolished nest building and retrieving components of maternal behavior, while crouching and nursing were unaffected. While few animals with these cuts were suckled when presented with pups the prolactin secretion response was undiminished when suckling did occur. Whereas previous studies have demonstrated that extensive surgical separation of the medial preoptic area-anterior hypothalamic continuum from the lateral preoptic area-lateral hypothalamus disrupts all aspects of maternal behavior, the present study has determined more specifically the zone of fibers essential for the active components of maternal behavior, i.e., nest building and retrieving. These fibers appear to enter/leave MPO dorsolaterally beneath the crossing of the anterior commissure in the region of the bed nucleus of the stria terminalis. These neural connections are not the same as those that regulate prolactin secretion in the lactating rat.

Animals↗
PubMed1978

Plasma progesterone levels during pregnancy and pseudo-pregnancy in the hare (Lepus europaeus syriacus).

A triphasic pattern of progesterone secretion was observed in female hares sampled throughout pregnancy and pseudopregnancy. After injection of hCG and artificial insemination (Day 1), progesterone values rose to a peak of 41.4 ng/ml about Day 14, remained at this level, then declined around Day 20 before increasing sharply to maximum levels of 67.7 ng/ml after midpregnancy (Day 28). Levels remained high for several days, then declined until Day 38, increased again until Day 41, before decreasing towards parturition. Progesterone levels were still high (37.5 ng/ml) 24h before parturition. The progesterone pattern during pseudopregnancy closely resembled that observed during the first half of pregnancy: levels rose from Day 2 to a peak at Days 11--18, then declined sharply to baseline levels around Day 22. It is suggested that the control of progesterone secretion might be transferred from the pituitary to the placenta at the beginning of the second half of pregnancy.

Animals↗
PubMed1978

Artificial insemination in the European hare (Lepus europaeus syriacus).

A simple technique for artificial insemination in hares was performed and used routinely in mass breeding of hares in captivity. Sperm was collected directly from the epididymides of males. Ovulation was induced by intravenous injection of human chorionic gonadotropin. Female hares were successfully inseminated throughout the year. Pregnancy occurred in 70% of inseminated females; the range in litter size was 1--3 offspring with a mean of 1.4. It was concluded that artificial insemination greatly simplified the breeding of hares in captivity.

Animals↗
PubMed1977

Chronic double lumen intravenous cannulation of the unrestrained rat.

Chronic double lumen intravenous cannulation was performed on the rat. The cannulation system consisted of a pulley assembly, protective tube, mounting post, and a double lumen cannula. Using a double lumen expanded catheter, a two-channel connection was made with the rat's vascular system through a single entry into the external jugular vein. The cannulation system permitted free animal movement in a large cage and simultaneous measurement of behavioral and physiologic variables. The procedure minimized stress and provided a simple alternative to other systems using two cannulas.

Animals↗