ADVERTISEMENTS:
In this article we will discuss about the meaning and stages of oestrus cycle in female vertebrates.
Meaning of Oestrus Cycle:
During breeding season the vertebrate female undergoes hormonal changes influencing reproductive organs, inducing histological changes leading to development of eggs. The cycle is called Oestrus cycle. In this period the female permits sexual mating. This is called heat-period or oestrus.
The period from the beginning of one heat to the next is oestrus cycle. Animals having only one oestrus cycle are monoestrus. Those with many cycles in the same breeding season at short intervals are polyoestrus. Rats, mice, sheep, etc. are polyoestrus.
ADVERTISEMENTS:
The changes in the histology of the female reproductive organs in vertebrates occur regularly in the oestrus cycle. Cyclical changes in the secretion of hormones from pituitary, gonad, uterus, etc. sponsor such changes. From the histological changes in the vaginal epithelium, different stages of the oestrus cycle are identified.
The vaginal epithelium is torn down and rebuilt cyclically, fluctuating between the stratified epithelium and low cuboidal epithelium. These cyclical changes can be ascertained by stained vaginal smear preparation for consecutive days in rat Rattus norvegicus and Rattus rattus.
Stages of Oestrus Cycle:
Ovarian and vaginal changes occur cyclically during oestrus cycle in four sub-stages:
(1) Proestrus,
ADVERTISEMENTS:
(2) Oestrus,
(3) Meta-oestrus and
(4) Di-oestrus.
1. Proestrus:
Duration about 12 hrs.; follicles grow faster; nucleated epithelial cells appear.
2. Oestrus:
Duration about 30 hrs.; follicles become larger; ovulation occurs; cornified squamous cells appear.
3. Metaoestrus:
About 6 hrs. duration; corpora lutea formed; leucocytes among cornified squamous cells appear.
ADVERTISEMENTS:
4. Dioestrus:
Duration about 50 to 55hrs; corpora lutea is formed; nucleated epithelial cells and leucocytes appear.
Cornified cells begins to disappear following di-oestrus or anoestus stage:
Procedure:
ADVERTISEMENTS:
a. Acclimatize female white rats (Sprague-Dawley strain) of 12-14 weeks age group for 7 days in animal house by keeping them in a suitable rat cage with recommended quantity and quality of food and water. The temperature and humidity of the animal house should be maintained as per recommendation of the “Ethical committee”.
Vaginal Smear Preparation:
Fix a time schedule for taking vaginal smear. Record serial numbers, date and time with a glass marking pen on one surface at one edge of the glass slides.
a. Introduce through the vagina about 0-5 ml normal saline solution with the help of a Pasteur pipette.
ADVERTISEMENTS:
b. Slowly draw out the vaginal swab slowly with the same pipette.
c. Put a drop of swab at the centre of the marked surface of the glass slide and make a thin smear.
d. Put the slide on a staining and fixing tray and allow to dry in air. Cover the semidried smear with methanol for fixing. Cover the whole set properly and leave for 10 minutes.
e. The fixed smear is double-stained with haematoxylin and eosin. Make the preparation permanent following standard technique for histological studies. The histological elements are studied with a microscope under low and high magnification. Draw figures of cellular elements.
ADVERTISEMENTS:
f. Repeat the above procedure for different stages of oestrus cycle to get a full picture of the whole cycle.
Observation:
Cellular elements in different stages of oestrus cycle (Fig. 31.1).
1. Proestrus stage:
Smear contains non-cornified nucleated epithelial cells.
ADVERTISEMENTS:
2. Oestrus stage:
Smear contains cornified epithelial cells.
3. Metaoestrus stage:
Leucocytes present among cornified epithelial cells.
4. Dioestrus stage:
High concentration of leucocytes.
