Morphological characteristics of ovaries as factor of possible influence on characteristics of sexual cycle in the mare

Abstract

The sexual cycle, endocrine regulation of estrus and the ovarian morphology of the mare are characteristic. Have these characteristics acquired through evolution in the mare remained preserved to this day in this animal specie which is 60 million years old and whose fossil remains date back to early Cenozoic, the earliest geological period in the development of the Earth and why? Hypothalamus neurons, cells of the pituitary and target organs, as genetically programmed for specific responses to steroid hormones, the photoperiod and the environmental factor, have an essential role in the regulation of the transcription of target genes, and regulatory proteins have been conserved in the course of evolution. The memory of these cells was acquired through evolution and the programmed gene expression can be modulated temporarily or permanently, through steroid hormones. Having in mind the extremely complex endocrine regulation of estrus in the mare, we wished, by clarifying the elementary structure of the mare ovaries, to contribute to the better understanding of this problem and the specificities occurring in this specie during the reproductive period. The problems in considering data dealing with the sexual cycle of mares and the appearance of ovaries are in the lack of the possibility to make up statistically relevant experimental groups for this specie, so that any data suitable for comparison is significant. The conventional manner of histological investigations and drawing of conclusions are rendered difficult by the specific morphological structure, where the ovarian medulla is on the periphery of the organ and the cortex distributed in the center and grouped around the ovulation fossa, the size of the ovary that reaches 6-9 cm follicles that are up to 7 cm, corpora lutea 1-2 cm in dimension, the specific tissue structure, the discrepancies in the size and appearance.

Polni ciklus, endokrina regulacija estrusa i morfologija jajnika kobile su osobeni. Da li su, i zbog čega, evolucijom stečene te karakteristike kobile ostale očuvane i danas kod ove vrste životinja koja je stara 60 miliona godina i čiji fosilni ostaci datiraju iz ranog kenozoika, najmlađeg geološkog doba razvoja zemlje? Neuroni hipotalamusa, ćelije hipofize i target organa, kao genetski programirane za specifične odgovore na steroidne hormone, foto-period i faktore sredine, imaju bitnu ulogu u regulaciji transkripcije target gena, a regulatorni proteini su konzervisani u toku evolucije. Memorija ovih ćelija, sticana je tokom evolucije, a programirana ekspresija gena, može da bude modulirana privremeno ili permanentno, pomoću steroidnih hormona. U razmatranju podataka koji se bave polnim ciklusom kobila i izgledom jajnika problemi su u nemogućnosti sačinjavanja statistički relevantnih eksperimentalnih grupa za ovu vrstu, pa je značajan svaki podatak pogodan za poređenje. Specifična morfologija sa medulom jajnika koja je na periferiji organa i korteksom raspoređenim u centru i grupisanim oko ovulatorne fose, veličina jajnika koja dostiže 6-9 cm folikuli veličine do 7 cm, žuta tela dimenzija 1-2 cm, posebna struktura tkiva, diskrepancije u veličinu i izgledu otežavaju klasičan način histoloških ispitivanja i donošenje zaključaka.