Archivos de biologia y medicina experimentales最新文献

Three-dimensional measurements of eleven kinds of cells, obtained from serial sections of five different organs, excised from eleven adult mammals of different body sizes-from a 40 g mouse to a 450 kg cow-were made. In order to minimize technical errors all organs were submitted to standardized fixation and staining procedures. Twenty cell diameters (at the nuclear level) were measured in each of the 7 microns serial tissue section which were made in two planes, after a 90 degree rotation of the fixed and embedded organ specimens. The mean values of the cell diameter measurements were submitted to a cluster analysis by means of a computer program, to establish the cell type groups with similar morphometric characteristics. The dendrograms of the cell-type groupings were then compared with the results obtained by applying the traditional statistical analysis of the cell sizes (in micrometers) in the three dimensions of space, and also with the principal component analysis. With the three statistical methods we came to analogous conclusions. The empirical allometric exponents for the three cell diameters, when expressed independently as functions of body mass, are not significantly different from zero, and in consequence cell sizes are independent of body mass. The physiological meaning of the body-size-independence of the mean three cell diameters is discussed.

Mammalian sperm capacitation and the acrosome reaction (AR) are essential prerequisites for fertilization. This report examines part of the molecular events developed during capacitation and the AR of mammalian spermatozoa; especially those events related to sperm head membrane bound enzymes and phospholipids. For this purpose, it has been analysed results obtained from an in vitro capacitation/acrosome reaction inducing system for golden hamster spermatozoa. First of all, the analysis is focused in the phospholipid transmethylation reactions possibly occurring at plasma membrane level during capacitation and the AR; it is suggested too, that this pathway could provide the substrate for a sperm head membrane bound phospholipase A2 which is able to produce a lysophospholipid (a fusogen) and fatty acids; both of them, very likely involved in the late steps of the AR. These assumptions are confirmed by experiments demonstrating that exogenous lysophospholipids and/or cis-unsaturated fatty acids are able to accelerate AR in previously capacitated spermatozoa. It is also suggested future research in this field, which could involve a sperm phospholipase C specific for phosphatydil-inositol, 4.5 bisphosphate; its products, Inositol trisphosphate and diacylglycerol could act as second messengers with a probable physiological function during capacitation. Finally, an integrative mechanism for the AR-involving phospholipid methylation, acrosin activation, phospholipase A2 activation and endogenous lysophospholipids and fatty acids production is proposed as a model for discussion.

Chalones are physiological inhibitors of cell proliferation that act either at the G1 or G2 phase of the cell cycle. They have been described for a variety of tissues, including the seminiferous epithelium. In vivo and in vitro characterization of rat G1 spermatogonial chalone demonstrate that it is a glycoprotein, heat-labile, molecular weight under 5,000 D, tissue specific but not species-specific, active at physiological pH, with a mechanism of cell action mediated by cyclic AMP. The origin of the substance are the differentiated cells of the spermatogenesis from primary spermatocytes up to round spermatids. The target cells are the type A (and perhaps only the A0) spermatogonia. The inhibitory effect, measured as a decrease in the uptake of H3-thymidine into testicular DNA, is not dependent on testicular steroids, Sertoli cell products (inhibin or the like) nor on the hypothalamic-hypophyseal-gonadal axis, since it occurs in vitro. In the mouse, the biological half-life (in vivo) of the G1 spermatogonial chalone is around 14 hs. Chronic administration for the entire length of mouse spermatogenesis does not alter spermatogenic kinetics nor does it result in azoospermia. The biological effect of the G1 spermatogonial chalone can be counteracted in vitro by means of an immune rabbit serum raised against a partially purified rat testicular extract (source of the chalone).

The gamete membrane fusion test, that uses zona-free hamster oocytes to evaluate the fertilizing ability of human spermatozoa, is being widely used in andrologic laboratories throughout the world. This test evaluates several steps of the reproductive process such as: a) sperm capacitation; b) acrosome reaction; c) gamete membrane fusion; d) sperm chromatin decondensation; e) chromosome condensation; f) egg activation as measured by the cortical granule breakdown and completion of meiosis. This test does not evaluates the sperm transit from the vagina to the site of fertilization nor the sperm passage through the human egg vestments. However, the sperm transit has been partly solved by the use of naturally occurring human cervical mucus to obtain seminal plasma free spermatozoa. This latter technique has greatly increased the diagnostic value of the gamete membrane fusion test. Notwithstanding, the results obtained with this test can vary considerably among the different laboratories, because of variations in the experimental design of the test. These differences can have an important effect upon the attitude the scientist and/or the physician might take in a given case of infertility. The parameters that vary most among the different laboratories are: a) obtention of seminal plasma-free spermatozoa; b) sperm concentrations; c) sperm preincubation time; d) type and concentration of serum albumin used. The original objective of this test was to evaluate the fertilizing ability of spermatozoa of men with problems of infertility. Nowadays is being also used for the assessment of male infertility agents and drugs that might affect the human reproductive function. The correlation found between the results of the gamete membrane fusion test with fertility has resulted in its use in testing the fertilizing ability of bovine and equine spermatozoa.

Semen analysis has been studied in 9 healthy adult males from sea level (150 m), age 19-32 years old and 15 healthy males from high altitude (NA), 9 from Cerro de Pasco (4,300 m) and 6 from Morococha (4,540 m), ages 19-45 years old. Five patients with chronic mountain sickness (MMC), whose ages ranged from 23 to 52 years old were also studied. The volume and motility were similar in NA and MMC, however both were below than in sea level subjects, but still in the normal range; the number of spermatozoa per 1 ml was lower at sea level than in NA and MMC, although the total number was higher at sea level due to the higher semen volume. Fructose at sea level was 356 +/- 53 mg/100 ml (mean +/- S.E.) which is similar to NA 237 +/- 45 whereas a MMC was significantly lower, 142 +/- 60. Citric acid was lower at sea level than in NA and MMC. Na, K and Cl, were similar among the three groups. The lower concentration of fructose in MMC parallels the decreased testicular function already found in these groups. However it is worthy to point out that the fertility is preserved in all the groups. The normal reproductive function in MMC is against the concept that this process occurs as a consequence of environmental disadaptation.

In this paper we review the mechanisms underlying the control of gonadotrophin (Gn) release and present evidences of the existence of a luteinizing hormone release-inhibitory factor. We have extracted and partially characterized this factor from rat hypothalamus and bovine median eminence. Our data indicate that the factor is a peptide that has a common antigenic determinant with GnRH, but is of smaller molecular weight than GnRH (750 daltons approximately). These facts strongly suggest that it may be a fragment of the GnRH molecule. The synthetic fragment GnRH (1-5) has similar biologic effects and molecular weight to those of the inhibitory factor obtained from the median eminence and hypothalamus. GnRH (1-5) has been shown to be produced in vitro by cleavage of GnRH by an hypothalamic endopeptidase. Based on this evidences, we suggest that the inhibitory peptide found by us is formed in vivo by degradation of GnRH. Moreover, we suggest that this factor may play a role on the regulation of LH release induced by GnRH.