The document discusses proestrus physiology in dairy cows and the two-cell, two-gonadotropin theory in reference to the male reproductive system. For dairy cows, proestrus lasts 2-3 days and marks the regression of the corpus luteum from the previous cycle. Rapid follicle growth occurs due to increasing FSH levels, estrogen levels begin to rise, and a preovulatory LH surge happens at the end of proestrus. The two-cell, two-gonadotropin theory states that in males, LH stimulates thecal cells to produce androgens while FSH stimulates granulosa cells to produce estrogens. Gonadotrop

1. AGRICULTURE AND FORESTRY UNIVERSITY
FACULTY OF ANIMALS SCIENCE, VETERINARY SCIENCE
AND FISHERIES (FAVF)
RAMPUR, CHITWAN
ASSIGNMENT ON TOPIC PROESTRAL PHYSIOLOGY IN DAIRY
COWS AND 2-CELL, 2-GONADOTROPIN THEORY IN REFERENCE
TO MALE REPRODUCTIVE SYSTEM (TESTES)
Submitted by
Ramesh Prasad Joshi
M.V.Sc Theriogenology (1st
sem)
Department of Veterinary Theriogenology
Roll no:VGO-M-06-2021
Submitted to
Dr. Bhuminand Devkota
Professor at Agriculture and Forestry University
Director, Directorate of Post Graduate Program
Department of Veterinary Theriogenology

2. Q. N. 01. Proestrus Physiology in dairy cow
The estrus cycle of cow starts from puberty and occurs approximately every 21 days. It has four
phases i.e. proestrus, estrus, metestrus and diestrus. The interval between the regression of the
corpus luteum from the previous cycle and estrus is known as the proestrus. The follicular
development was translated by the proestrus phase. Proestrus lasts for two to three days and is
defined by the CL regressing and the ovulatory follicle entering its last growth phase. As blood
progesterone levels fall, LH and estrogen positively feedback on one another, causing the
ovulatory follicle to produce more estrogen quickly, which raises blood concentrations of both
hormones. Treatment with PGF2 would not interfere with the animal's typical return to estrus
because the CL is already experiencing regression at this point (Larson & Randle, n.d.)
Figure: Overview of an estrous cycle
Figure: Hormonal changes during follicular phase

3. Different events that occurs during proestrus phase of estrus cycle;
 Rapid follicle growth occurs during proestrus due to increasing FSH levels
 Estrogen levels begin to increase
 At the end of proestrus, the animal begins to show signs of estrus
 Preovulatory LH surge occurs
Figure:Schemetic diagram of preovulatory LH surge
Decrease P4 from CL
Increase GnRH
Increase FSH and LH
Increase Inhibin Decrease FSH
Proestrul follicular
development
Increase Estradiol to
threshold
Preovulatory LH surge

4. Q.N. 02: Two cell two gonadotropin theoryin reference to male reproductive system (Testes)
Figure: Two cell two gonadotropin model theory in male animals
According to the two-cell-two-gonadotropin theory, luteinizing hormone stimulates thecal cells to
produce androgens, while follicle-stimulating hormone stimulates granulosa cell to produce estrogens
from androgens. Follicle-stimulating hormone is considered to have minimal influence on thecal-cell
androgen production (Barnes et al., 2000). Steroids are produced from cholesterol via the cooperative
actions of theca and granulosa cells. LH binds to the luteinizing/chorionic gonadotropin receptor
(LH/CGR) on the cell surface, stimulating the development of the steroidogenic enzymes required for
androgen synthesis (Rivera Craig, 2009).
Gonadotropin-releasing hormone (GnRH) secreted by the hypothalamus stimulates the pituitary gland to
generate follicle-stimulating hormone (FSH) and luteinizing hormone (LH), two gonadotropins required
for gonadal development. FSH and LH are heterodimers containing a common subunit alpha and two
distinct subunits beta. After production from the pituitary gland, these hormones bind to particular
receptors, FSH receptor (FSHR) and LH receptor (LHR), in gonadal somatic cells to control the
secretion of sex steroid hormones such as testosterone, estrogen, and progesterone (Kitano et al., 2022).
The rate-limiting enzyme for androgen synthesis, cytochrome P450 family 17 subfamily A member 1
(CYP17A1), is stimulated by LH specifically in the theca cells of the ovary. This results in the
production of androgens, mostly androstenedione. The aromatase enzyme, which is encoded by the
Cyp19 gene, regulates the conversion of androgens from the theca cell to the ovarian granulosa cell and
allows them to easily diffuse there. FSH controls how much Cyp19 is expressed in granulosa cells.
Theca cells generate androstenedione, which diffuses into granulosa cells and is converted to
Hypothalamus (Adenohypophysis)
Theca cell Granulosa cell
LH (Leuteinizing Hormone) Androstenedione
Cholesterol Androstenedione Testosterone
Multistep
Estradiol Effects

5. testosterone by the enzyme 17-hydroxysteroid dehydrogenase (HSD17B) or estrone via aromatase
(CYP19A1). CYP19A1 converts testosterone into 17-estradiol. However, utilizing estrone as a substrate,
HSD17B may also produce 17-estradiol (Wu et al., 2019).

6. References:
Barnes, R. B., Rosenfield, R. L., Namnoum, A., & Layman, L. C. (2000). Effect of Follicle-Stimulating
Hormone on Ovarian Androgen Production in a Woman with Isolated Follicle-Stimulating
Hormone Deficiency. New England Journal of Medicine, 343(16), 1197–1198.
https://doi.org/10.1056/nejm200010193431614
Kitano, T., Takenaka, T., Takagi, H., Yoshiura, Y., Kazeto, Y., Hirai, T., Mukai, K., & Nozu, R. (2022).
Roles of Gonadotropin Receptors in Sexual Development of Medaka. Cells, 11(3), 1–11.
https://doi.org/10.3390/cells11030387
Larson, R. L., & Randle, R. F. (n.d.). The Bovine Estrous Cycle and Synchronization of Estrus.
Rivera Craig, Z. (2009). Characterization of residual ovarian tissue in 4-vinylcyclohexene diepoxide-
treated mice following ovarian failure. Doctor of(March).
Wu, S., Xue, P., Grayson, N., Bland, J. S., & Wolfe, A. (2019). Bitter taste receptor ligand improves
metabolic and reproductive functions in a murine model of PCOS. Endocrinology, 160(1), 143–
155. https://doi.org/10.1210/en.2018-00711