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Biomedical subjects

L Yogev

Publications and source records attributed to L Yogev.

At least 73 records · Page 4Linked to original sources
PubMed1991

Sperm motility index: a new parameter for human sperm evaluation.

OBJECTIVE: The study was performed to evaluate the correlation between sperm motility index, a novel parameter of semen quality, and routine semen analysis parameters by microscopic evaluation. DESIGN: Sperm motility index was measured by an electro-optical device, the Sperm Quality Analyzer (United Medical Systems Inc., Santa Ana, CA). Human semen samples covering the whole span of qualities were analyzed prospectively and simultaneously by both methods. SETTING: Samples were collected from patients referred to university hospital infertility clinics. PATIENTS, PARTICIPANTS: Nine hundred sixty-eight semen samples of 812 patients and healthy men were analyzed. MAIN OUTCOME MEASURE(S): Sperm motility index is a measurement of optical density fluctuations caused by motile cells; therefore, a positive correlation was anticipated between its values and semen motility parameters. RESULTS: Sperm motility index values demonstrated statistically significant correlation with motile cell concentration, total cell concentration, and percent motile cells. They were also shown to reliably represent semen quality assessment obtained by two experienced andrologists. CONCLUSIONS: The sperm motility index provides a reliable and objective reflection of semen motility parameters and quality.

Autoanalysis↗
PubMed1990

Transferrin in seminal plasma and in serum of men: its correlation with sperm quality and hormonal status.

Transferrin concentrations in the seminal plasma and in serum were measured and correlated with sperm quality (concentration, motility and morphology) and hormonal status (FSH, LH and testosterone) of 75 men aged from 21 to 46 years. A significant positive correlation was found between the seminal plasma concentration of transferrin and the sperm concentration (r = 0.69, P less than 0.0001) and motility (r = 0.39, P less than 0.0001). No other correlations were found. These data confirm that seminal plasma levels of transferrin can be used as a reliable index of sperm quality, and possibly as a Sertoli cell marker.

Adult↗
PubMed1990

Determination of urinary luteinizing hormone for prediction of ovulation.

Detection of the approximate time of ovulation is important in the in vitro fertilization-embryo transfer programs in order to avoid a possible early surge of luteinizing hormone (LH) before human chorionic gonadotropin administration in the induction of ovulation and for timing of artificial insemination. In the present study correlation between the detection of LH in urine and serum levels (mean +/- SEM) of estradiol greater than 557 +/- 118 pg/ml, progesterone less than 1.9 +/- 0.37 ng/ml and leading follicle diameter greater than 26.2 +/- 1.3 mm (mean +/- SEM) was found. Thus, the prediction of ovulation via detection of urinary LH in urine by a dipstick procedure is a good semiquantitative method, accurate enough, reliable, cheap and acceptable by the women.

Clomiphene↗
PubMed1990

Luteinizing hormone secretion as a response to a second naltrexone administration.

Previous studies with naltrexone (Nalt), a "long-lasting" opioid antagonist, demonstrated a rapid increase in luteinizing hormone (LH) secretion which gradually declined, reaching baseline values after 1 hr. A second Nalt challenge, 120 min later, caused only a blunted response. This poor reaction has been shown in this study not to be due to lack of pituitary responsiveness, because LH-releasing hormone treatment revealed a normal response. A time-response study was carried out in order to establish the refractory period length, by administering a second Nalt injection at 0 hr (immediately after the first injection) and at 2, 4, 8, 16, and 24 hr after the first bolus. Partial responsiveness could be achieved 2 and 4 hr after the first challenge. However, only after 8 hr was a full response recorded. The diurnal changes in serum LH (nadir at 18.00 hr) did not affect the response to Nalt challenge. It is suggested that in the presence of a Nalt blockade, nonopioid systems are able to "normalize" LH blood levels. However, when Nalt blood levels have fallen sufficiently to allow the endogenous opioid system to take primary control again, then a second Nalt injection will provoke a renewed response.

Animals↗
PubMed1989

Possible dopaminergic system involvement in LH and PRL responses to naltrexone treatment.

Naltrexone (Nalt) causes a rapid increase in luteinizing hormone (LH) level. This short term increase of LH concentration declines to baseline levels in less than 1 hour. Addition of pimozide (0.1 mg) caused a blunted response to Nalt challenge, with significantly reduced LH peak values compared with Nalt treatment alone. Pimozide alone caused a delayed decrease compared with baseline LH values. By following plasma prolactin (PRL) levels it was shown that pimozide administration increased PRL levels rapidly for more than 2 hours. Addition of Nalt to pimozide-treated rats significantly decreased plasma PRL values compared with pimozide alone. Nalt injected by itself attenuated PRL baseline levels. Thus, the mechanism by which pimozide caused PRL elevated level is via the dopaminergic as well as the opioid system. It is suggested that the opioid system controls plasma PRL and LH levels through other hypothalamic neurotransmitters in addition to dopamine.

Animals↗
PubMed1988

Clomiphene citrate treatment in oligozoospermia: comparison between two regimens of low-dose treatment.

Clomiphene citrate (CC) is a well-known drug in fertility clinics that is used for increasing gonadotropin secretion. The present study was planned in order to evaluate the efficiency of a new regimen of treatment by 25 mg on alternate days (group A), compared to a daily dose of 25 mg (25 days on, 5 days off, group B), for 4 months. Semen quality was assessed in two matched groups, which consisted of 45 and 44 normogonadotropic oligoterato-asthenozoospermic (OTA) men, respectively. Nine men in group A and 22 in group B did not respond to therapy by improvement in semen quality. The statistical evaluation of the results revealed group A to yield the highest improvement in sperm concentration (P less than 0.0008) and total sperm count (P less than 0.004). Sperm motility was improved only in group A. No changes were recorded in the morphology of the sperm cells or in semen volume. Pregnancy rate after 6 months of follow-up was 26.7% and 20.5%, in couples of groups A and B, respectively. This study implicates the use of CC (25 mg on alternate days) in andrologic clinics as one of the recommended drugs for normogonadotropic OTA subfertile men in order to achieve a significant increase in sperm concentration and total sperm count.

Adult↗
PubMed1987

Opiate system involvement in the control of LH secretion in diabetic and normoglycemic male rats.

The effect of Naltrexone (Nalt), a specific opiate receptor blocker, on LH secretion was studied at frequent intervals during the first hour following treatment. Nalt was injected i.v. by one bolus (1 mg/rat) to diabetic and normoglycemic rats. Blood samples (0.8 ml) were withdrawn at short intervals after injection, through an indwelling cannula. The diabetic rats responded by secretion of LH, which was lower, but not significantly, than that of normal rats, (peak levels 0.74 +/- 0.17 and 0.97 +/- 0.21 ng/ml respectively). After 45 min., LH levels were in the same range as baseline level in the diabetic group; but were still significantly elevated in the control rats. Thus, it can be concluded that in normal rats, as well as in diabetics, LH secretion as a response to Nalt was episodic in spite of Nalt's long half life time. In order to explain the rapid fall in LH levels after Nalt administration, normal rats were injected with a second bolus of Nalt, 2 hours after the first. The second bolus caused only a blunted response of LH secretion. In another experiment, administration of morphine (1 mg/rat) 2 hours after pretreatment with Nalt did not stimulate the prolactin secretion which normally follows morphine treatment. These results indicate that the rapid decrease of LH levels after Nalt treatment in normal rats is not due to absence of the drug in the system. It is suggested that other neural mechanisms, such as the dopaminergic system, are activated during Nalt influence.

Animals↗
PubMed1987

Patterns of reproductive hormone secretion in hibernating Turkish hamsters.

Changes in gonadal state and in circulating reproductive hormones [follicle-stimulating hormone (FSH), prolactin (PRL), and testosterone] were studied for 30 wk in male Turkish hamsters (Mesocricetus brandti) induced to hibernate by exposure to a short-day, cold environment [10:14-h light-dark (LD) cycle, 6 +/- 1 degree C]. Similar measures were compared in hamsters maintained under short-day warm conditions (10:14-h LD, 21 +/- 2 degrees C). A decrease in testicular size and in hormone levels was observed after 9-12 wk of short-day exposure in all animals. After 24 wk, hormone levels rose again, accompanied by testicular recrudescence, in short-day warm hamsters and in hamsters that failed to hibernate in the cold. For animals that hibernated the temporal pattern of endocrine and gonadal changes differed only slightly in comparison. Testicular recrudescence of hibernators lagged approximately 3 wk behind that of short-day warm hamsters. Hormone levels were generally lower in hibernators sampled during bouts of torpor than during bouts of spontaneous arousal from torpor. A marked elevation of serum FSH was observed in aroused hibernators well before the end of the hibernation season (at 21 wk of short-day exposure). Mean testosterone and PRL values had increased by wk 27, after hibernation was terminated in the majority of animals. These results indicate that testosterone may not be essential for the termination of the hibernation season. The data also suggest that an endogenous timing mechanism, resistant to the decreased body temperature experienced during torpor, may function to trigger a resurgence of the neuroendocrine-gonadal axis at the end of the winter season.

Animals↗
PubMed1985

Changes in LH and prolactin levels in diabetic male rats and the role of the opiate system in the control of their secretion.

Diabetic male rat has low serum levels of luteinizing hormone (LH) and testosterone (T), which are accompanied by atrophy of the testes and accessory glands. The present study investigated changes in the serum levels of LH, prolactin (PRL) and glucose, following diabetes induction by streptozotocin. In addition, involvement of the opiate system in the control of LH and PRL secretion was evaluated. There was no difference in PRL levels between diabetic and control animals, except at 8 hours after streptozotocin injection. In contrast, the diabetic animals had consistently lower levels of LH, starting on the second day of diabetes. Blockade of the opiate system by naltrexone caused a sharp increase of LH levels in normoglycemic rats, while only a gradual decrease was observed in hyperglycemic animals. PRL secretion was inhibited by naltrexone, both in diabetic and control groups. It is concluded that, unlike normoglycemic rats, inhibition of LH secretion in diabetes is not under the control of the opiate system, probably as a result of T deficiency. In contrast, PRL secretion in diabetic rats, as in the control group, is under the influence of endogenous opiates.

Animals↗
PubMed1985

Adrenal corticoids in hamsters: role in circadian timing.

The 24-h patterns of circulating cortisol and corticosterone were determined in male hamsters housed under a 14:10 light-dark cycle. Corticoid levels varied significantly over the 24-h sampling period with peak levels of both hormones occurring near the onset of the daily dark phase. The ratio of cortisol to corticosterone changed dramatically during the day. Corticosterone levels were significantly higher than cortisol during the early part of the light phase; however, cortisol levels became significantly higher than corticosterone when both hormones began their daily rise. To examine whether the circadian rhythm of cortisol secretion could be involved in the physiological control of hamster circadian organization, cortisol was infused at approximately physiological levels into adrenalectomized hamsters either continuously or in a 24-h rhythm. No significant differences were observed in the timing of circadian wheel-running rhythms in hamsters housed in LD 16:8, LD 14:10, or LL when cortisol was infused continuously, in a 24-h rhythm that mimicked the cortisol rhythm of intact hamsters, or in a 24-h rhythm several hours out of phase with the rhythm of intact hamsters. Provision of cortisol in a 24-h rhythm appeared to promote the survival of adrenalectomized hamsters since hamsters receiving a 24-h pattern of cortisol survived the experimental protocol significantly longer than those receiving the same dose of cortisol continuously.

Adrenal Cortex Hormones↗
PubMed1985

Components of the rat conceptus that account for prolactin inhibition.

The secretions from developed concepti in the rat appear to inhibit both the rhythmic nocturnal secretion of prolactin (Prl) during the second half of pregnancy and the neurally mediated Prl release in response to suckling stimulation. In order to identify the parts of the concepti capable of inhibiting Prl secretion, the components of the concepti were systematically removed and their effect on plasma Prl levels was examined. In the first experiment, female rats which were simultaneously pregnant and lactating were tested for Prl secretion in response to suckling stimulation after one of the following treatments: 1) removal of the foetuses only, 2) removal of the foetuses and trophoblasts, 3) removal of the complete concepti. In the second experiment, pregnant rats were tested for the presence of nocturnal Prl surges after either removal of the foetuses and trophoblasts or removal of the entire concepti. The results indicate that after removal of the foetuses alone, the inhibition of Prl secretion remains. Following removal of both the foetus and the trophoblast, leaving the decidua in situ with a supplementary progesterone implant, the decidua still retain a partial capacity to inhibit Prl secretion in response to suckling stimulation, while their inhibitory effect on the nocturnal Prl surges was very minute. Degeneration of the decidua occurred following the removal of the trophoblast, when no exogenous progesterone was supplied. The deterioration of the decidua or total removal of the concepti eliminates the entire inhibition of Prl secretion, both on the nocturnal surges as well as in response to suckling stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Effects of timed melatonin infusions on reproductive development in the Djungarian hamster (Phodopus sungorus).

In confirmation of earlier work, daily melatonin infusions of 9- or 12-h duration inhibited testicular development in pinealectomized juvenile Djungarian hamsters, while daily infusions of 6-h duration did not prevent gonadal growth. Two other methoxyindoles (5-methoxytryptophol and 5-methoxytryptamine) had less than 4% of the activity shown by melatonin. When pinealectomized hamsters received two short duration (i.e. 3, 5, or 6 h) melatonin infusions each day, gonadal development was not inhibited if the two daily infusions were separated by a period of 2 or 3 h without melatonin treatment. Thus, the effects of separate pulses of melatonin were not additive in this paradigm. When single, short duration daily infusions of melatonin (5-h) or isoproterenol (6-h) were administered to pineal-intact hamsters, gonadal inhibition occurred only when the infusions were given at times that would lead to an expected overlap with and extension of the endogenous nocturnal melatonin peak. Significant inhibition of testicular growth could be obtained with as few as 2-4 days of melatonin treatment. These observations further support the importance of melatonin peak duration and also indicate other interesting temporal aspects of melatonin action in the Djungarian hamster.

Aging↗
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↗
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

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↗