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PubMed1989

[Possible involvement of the renin-angiotensin system in reproduction. II. Occurrence and role in the female reproductive tract].

Biochemical and immunological studies of the last years reveal the existence of an "ovarian renin-angiotensin system (RAS)". Despite of the low angiotensin-conterting enzyme (ACE) activity in the ovary the follicular fluid is rich in angiotensin II (AII). The detection of AII receptors on cells within maturating follicles proves them as AII targets. Therefore, it is supposed that AII may be involved in the regulation of fundamental processes of follicle maturation and/or corpus luteum formation. Further interesting findings are the high concentration of prorenin in the follicle fluid of women causing an increase of the prorenin blood plasma level at time of ovulation, and a second increase of the blood prorenin concentration in the middle of the luteal phase. With respect to the ACE activity in the ejaculate it is imaginable that the smooth muscle tonus of the uterus and the oviduct could be affected by local generation von AII and/or degradation of bradykinin and thus the transit of the semen may be facilitated. Further systematic research is necessary to bring more light into the physiological context and to replace hypothetical interpretations of the findings by exact knowledge.

Animals↗
PubMed1987

Effects of zeranol on reproduction in beef bulls: scrotal circumference, serving ability, semen characteristics, and pathologic changes of the reproductive organs.

Effects of zeranol on scrotal circumference, serving ability, semen characteristics, and postmortem measurements of the genital organs were determined in beef bulls from 9 to 20 months of age. Group 1 (n = 5) served as a nonimplanted control group. Group 2A (n = 5) was implanted with 36 mg of zeranol at birth and at 3 and 6 months of age. Group 2B (n = 5) was implanted with 36 mg of zeranol every 3 months from birth through 18 months of age. Scrotal circumference was adversely affected by zeranol in groups 2A and 2B, but values approached those of group 1 with increasing age. Serving ability was also affected adversely but tended to recover with increasing age. Semen quality was low in groups 2A and 2B and did not improve with increasing age. There was no difference in testicular weight, vesicular gland weight, and penis length among groups when bulls were slaughtered at 20 months of age. Epididymal weight was greater in group-2B bulls and was most likely a consequence of epididymal lesions. Histologic examination of the genital organs revealed that zeranol induced adenomyosis and sperm granulomas in the caudae epididymidis and markedly altered the structure of the sexual accessory glands of bulls in groups 2A and 2B. Alterations in the vesicular glands were characterized by reduced alveolar development and an increase in connective tissue. Low epithelium associated with focal areas of squamous metaplasia were common in the prostate of groups 2A and 2B bulls. Lesions in the bulbourethral glands were characterized by low glandular epithelium, focal areas of squamous metaplasia, cystic collecting ducts, and an increase in connective tissue. Groups 2A and 2B had more abnormal seminiferous tubules than did group 1. Lesions in groups 2A and 2B may have been direct effects of zeranol or may have resulted from reduced testosterone secretion.

Animals↗
PubMed1992

Reproductive activity of Synosternus cleopatrae (Siphonaptera: Pulicidae) in relation to host factors.

Reproductive activity of Synosternus cleopatrae (Rothschild) infesting Gerbillus andersoni allenbyi Thomas was studied in a natural setting in Israel. Rodents were trapped and measured (weight and length), their sex was identified, and their reproductive status estimated. Their ectoparasites were removed, and fleas were dissected and their oocytes measured. Two indices of flea reproductive activity were analyzed: "reproductive status," which distinguished between gravid and nongravid females, and "reproductive intensity," which was estimated as the sum over the two largest oocytes of the products of oocyte length multiplied by oocyte width. Both indices showed that no reproduction took place between November and January, but reproduction was relatively stable during the rest of the year. Although flea reproductive activity differed significantly among individual hosts, only a small fraction of gerbils (10-15%) carried a significantly different proportion of reproductive fleas than their monthly sample proportion (based on all fleas regardless of hosts). All these hosts carried a lower proportion of reproductive fleas than their monthly sample proportion. The host's sex, but not reproductive status or age, had a significant effect on flea reproduction, expressed as a higher reproductive activity on male gerbils. Infestation burden expressed as ectoparasite counts was included in the statistical analysis. Only lice, Polyplax gerbilli Ferris, but not S. cleopatrae, Stenoponia tripectinata (Tiraboschi), and a total of five mesostigmatid Acari had a significantly negative association with S. cleopatrae reproductive activity. These relationships between S. cleopatrae reproductive activity and the host infestation burden do not support the hypothesis of modulation of S. cleopatrae reproduction by the infestation burden. However, differences in the reproductive activity of ectoparasites between their hosts may play a major role to generate the parasite clumped distribution. Thus, gerbil males probably carry more fleas than gerbil females because of the higher reproductive activity of S. cleopatrae on gerbil males.

Animals↗
PubMed1983

Reproductive suppression among female mammals: implications for biomedicine and sexual selection theory.

Female mammals experience a very high and often unappreciated rate of reproductive failure. Among human pregnancies alone, over 50 per cent fail between conception and parturition, and the majority of these failures are unexplained. These findings present important problems for evolutionary theory as well as for health care practices. This paper addresses these high rates of reproductive failure among mammals, by extending the work of a number of evolutionary biologists regarding the reproductive consequences of environmental adversity. The basic model upon which we elaborate, termed the Reproductive Suppression Model, argues that females can optimize their lifetime reproductive success by suppressing reproduction when future conditions for the survival of offspring are likely to be sufficiently better than present ones as to exceed the costs of the suppression itself. These costs are a function of reproductive time lost and the direct phenotypic effects of the suppression itself. To evaluate the benefits and costs of suppression, the following types of cues should be assessed: the female's physical and mental health, her stage of reproduction, the physical and genetic status of her offspring, and the external conditions at the time of birth. We also examine various issues of social suppression, whereby the conditions for survival of offspring are a function of the reproduction and support of other group members. Under such conditions, some females may be able to improve current conditions for reproduction by suppressing the reproduction of others. Field data from our own work are presented, describing socially mediated reproductive competition among continuously breeding female yellow baboons and among female hoary marmots. Social suppression in other mammals is also evaluated, including that in human beings, and we conclude with some implications of the Reproductive Suppression Model for sexual selection theory regarding female-female reproductive competition, as well as human health care.

Abortion, Spontaneous↗
PubMed1984

Grading and rotational crossbreeding of beef cattle. I. Reproductive performance.

Purebred Angus (A), Polled Hereford (PH) and Santa Gertrudis (SG) bulls were mated to grades, two-breed and three-breed rotational crosses of these breeds (seven herds) to produce three generations (G1, G2 and G3) of calves. The grade A and PH cows were higher in A and PH breeding, respectively, than grade SG cows were in SG breeding. Reproductive performance among grade and rotational-cross herds was evaluated for herd differences, heterosis and effects of various genetic components. For cows that produced G1 calves, the proportion of cows that calved, had a live calf and weaned a calf was higher (P less than .01) for those that calved compared with those that failed to calve the previous year. For cows that produced G2 and G3 calves, previous year's calving status did not affect (P greater than .05) reproductive performance. Grade A and PH were similar (P greater than .05) in reproductive performance during G1, G2 and G3. As generations advanced, SG decreased in reproductive performance. Except for the PH-SG rotational cross in G3, the A, PH and all two-breed rotational crosses and the three-breed rotational cross generally were similar (P greater than .05) for the three reproductive traits during each generation. Within generations, reproductive performance was similar (P greater than .05) between rotations within each of the two-breed rotational cross herds. For the three-breed rotational cross herd, differences due to rotation generally were not significant during G1 and G2, but for G3, the SG sires were associated with lower (P less than .05) reproductive performance for each of the three reproductive traits compared with A and PH sires. Heterosis percentages generally were positive but not significant for each of the three reproductive traits. On the basis of additive and maternal effects of A and SG expressed as deviations from PH, the only genetic component that significantly affected reproductive performance was the detrimental additive effect of SG in G2 and G3 for each of the three reproductive traits. Also, there was a consistent negative relationship between breed additive and maternal components for each of the three reproductive traits during each generation. Only 4 to 7% of the variation in reproductive performance was accounted for in the analyses that included breed additive, breed maternal, heterosis and average maternal heterosis effects. Averaged over generations, from .1 to .4% additional variation was due to factors that may have included specific maternal heterosis, epistasis and linkage.

Animals↗
PubMed1992

Environmental cues, endocrine factors, and reproductive diapause in male insects.

Environmental cues, mostly photoperiod and temperature, mediated by effects on the neuroendocrine system, control reproductive diapause in female insects. Arrest of oocyte development characterizes female reproductive diapause, which has two major adaptive functions: It improves chances of survival during unfavorable season(s), and/or it confines oviposition to that period of the year that is optimal for survival of the eggs and progeny. Although reproductive diapause is less well studied in male insects, there may be no sex-dependent differences in regard to the first of these functions. The second one, however, is not valid for the male; instead, selection pressure directs the male's reproductive strategy toward maximum chances of fertilization of the female's eggs with minimum waste of energy. Therefore, in species with female reproductive diapause, the males may or may not exhibit diapause, but if they do, their diapause must be adapted to that existing in conspecific females. Male reproductive diapause is defined as a reversible state of inability of the male to inseminate receptive females. In relation to reproductive diapause, there are several patterns of coadaptations between male reproductive strategy and timing of female receptivity. (a) In some insects, the females are receptive in the early part of their diapause; mating occurs during this period and there is no diapause in the male. The male dies shortly after copulation and the female stores the sperms to fertilize the eggs that develop after termination of the female's diapause. (b) In some species, as in the grasshopper Anacridium aegyptium, females are receptive during diapause; though oocyte development is arrested, copulation occurs and the stored sperms fertilize the eggs when the female's diapause ends. Males were claimed to have no diapause, but recent studies have revealed the presence of a reproductive diapause in a proportion of the males. This and other cases show that female receptivity during reproductive diapause may or may not be accompanied by male reproductive diapause. If there is a reproductive diapause in the male, it is controlled by the same endocrine mechanism, the corpora allata (CA), as in the females. (c) In many species females are refractory during their diapause. In these cases, males exhibit reproductive diapause, which may be light, as in the beetle Oulema melanopus, or well established, as in certain grasshoppers, butterflies, and beetles. In the latter cases, male diapause is controlled by similar environmental cues (photoperiod, temperature) and by the same intrinsic mechanism (neuroendocrine system, especially CA) as female diapause.(ABSTRACT TRUNCATED AT 400 WORDS)

Adaptation, Physiological↗