115 ROLE OF THE OVARY AND UTERUS FOR THE PLAINS VISCACHA (LAGOSTOMUS MAXIMUS MAXIMUS, CHINCHILLIDAE) REPRODUCTION

A dogma of mammalian reproduction states that primordial germ cells in females are restricted to the intrauterine phase and only small portions of oocytes are available for ovulation during the adult life. Among the rare exceptions to this rule is the plains viscacha. It polyovulates up to 800 oocytes per cycle, from which 10 to 12 are implanted, but only 1 to 2 conceptuses survive. To better understand the main mechanisms involved in these patterns of super-ovulation, super-implantation, and embryonic loss in the viscacha, we conducted an analysis of the ovary and uterus of pregnant females and their conceptuses. Pregnant females (n = 16) of ~50 and 90 days of gestation (early to mid-gestation) were selected for conceptus recovery. Hemi-ovariohysterectomy was performed following surgical and anaesthetic protocols used for laboratory animals and the conceptuses collected. Female fetuses of Day 50 (n = 2) and 90 (n = 1) of gestation were obtained from Estación de Cría de Animales Silvestres, Buenos Aires, Argentina. The reproductive organs were investigated by means of gross morphology, histology (hematoxilin and eosin), stereology (quantification of the volume of the ovary and number of ovary follicles), immunohistochemistry (PCNA, Oct-4, VEGF, and Caspase-3), and transmission electron microscopy. In the Day 50 fetal samples, the ovaries had an ovoid shape with smooth surface without apparent folds. First steps of subdivision were observed in the ovary of fetus of 90 days. The total volume of all fetal ovaries was of 4.8 mm2 and a coefficient of variation (CV) of 0.32. The ovaries of adult individuals had remarkable invaginations with surface projections and were small, asymmetrical, and dorsoventrally flattened with a mean of 77.6 mm3 (CV = 0.47). Only adult females had differentiation of germ cells. Primordial follicles had a mean of 9.9 × 105 (CV = 0.19), representing 93% of the total number of ovarian follicles. The mean of primary follicles was 3.05 × 104 (CV = 0.36), whereas for secondary follicles it was 2.75 × 104 (CV = 0.50), each representing 3% of all ovarian follicles. The number of antral follicles in several stages of development was 8.64 × 103 (CV = 0.75), representing 1% of the follicles. Primordial follicles expressed pluripotency (Oct-4+) and proliferation (PCNA+) markers, as well as the primary follicles. The cells did not react for Caspase-3 as marker for apoptosis. Variations regarding to the vascularization of the different regions of the uterine horn were observed, which were more intense and efficient near to the cervix. Data showed that a specialised, highly convoluted structure of the ovarian cortex developed in the intrauterine phase as a prerequisite for massive super-ovulation, associated with the inhibition of apoptosis and continued proliferation of germ cells, as well as maintenance of several corpora lutea during the adult life. Thus, a highly complex pattern of polyovulation, polyimplantation, and controlling mechanisms has evolved in the female reproductive system of the viscacha that mainly was associated with the maternal side. After an in-depth analysis of the arterial and venous vascularization of the uterine horns and uteri, we speculate that specializations regarding the vasculature and musculature evolved first and then contributed as a compensatory or controlling mechanism for polyovulation and polyimplantation. In conclusion, polyovulation in the viscacha represents a unique enigma in reproductive biology.

Histological and histochemical study of the uropygial gland of chimango caracara (Milvago chimango vieillot, 1816)

The uropygial glands of birds are sebaceous organs that contribute to the water-repellent properties of the feather coat. We studied the histological and histochemical characteristics of the uropygial gland of chimango caracara using hematoxylin and eosin (H & E), Gomori´s trichrome, orcein, Gomori´s reticulin, periodic acid-Schiff (PAS), Alcian blue (AB) and a variety of lectins. The gland is composed of two lobes and a papilla with 20 downy feathers. It is surrounded by a capsule of dense connective tissue that contains elastic, reticular and smooth muscle fibers. The papilla is delicate and has two excretory ducts. The gland mass relative to body mass was 0.143%. Both adenomer cells and their secretions were stained with Sudan IV, PAS and AB, and were positive for numerous lectins that indicated the presence of lipids and carbohydrates. Immunohistochemical techniques to detect PCNA confirmed cell proliferation in the basal stratum of the adenomer cells. The lipids and glycoconjugates secreted by the uropygial gland serve numerous functions including protection against microorganisms.

Development of compensatory hepatic hyperplasia in mice carrying the hepatocellular carcinoma ES12a

In a previous paper we reported that the presence of the hepatocellular carcinoma SS1K in host mice resulted in an earlier appearance of the hepatocyte mitotic peak during liver regeneration after a partial hepatectomy as well as in an increase in the amplitude of that mitotic wave. In the present work we analyse the effect of another hepatocellular carcinoma, the ES12a (HCES12a). Adult male mice of the C3H/S strain standardised for circadian-periodicity analysis, were used. One group received a subcutaneous graft of the HCES12a tumor, while another group served as control. Fifteen days later, all animals were submitted to a partial (70%) hepatectomy at 10:00 h and beginning at 16:00 h lots of between 5 and 9 host and control animals each were sacrificed at 4 h intervals until 16:00 h on the third day thereafter. All mice were injected with 2 microg/g colchicine 4 hrs before killing, and samples of livers were processed for hematoxylin-eosin staining. We determined the hepatocyte mitotic index for each animal and the mean value +/- the standard error of the mean for each lot. The peak of mitotic activity in the tumor-bearing animals took place four hours earlier than in control mice but the average values of hepatocytic mitotic activity were similar in both groups

Effect of partial and sham hepatectomy on the growth of a hepatocellular carcinoma

We examined the effect of partial hepatectomy on the proliferation of hepatoma ES12a grafted into C3H/S mice compared to tumor growth in sham-hepatectomized controls. The animals were sacrificed every 4 hrs during three days from the 6th to the 78th h following each type of surgery. Unoperated tumor-bearing mice were likewise killed as controls, but only during one complete circadian period. All animals received 2 microg of colchicine per g of body weight intraperitoneally 4 hrs before decapitation. Measurement of mitotic indices in hematoxylineosin-stained tumor samples revealed a decrease in proliferation and a modification of the diurnal mitotic-activity profile in the hepatectomized and sham-operated animals from the first day after surgery. These differences persisted by the third postoperative day only in the hepatectomized animals. Thus, although surgical stress may initially affect tumor growth, the latter results must be the effect of the influence of the hepatic regeneration.