1. Introduction

Progesterone is the hormone responsible for maintenance of pregnancy. The primary source of progesterone is the corpus luteum of the ovary.

Progesterone can also be produced, but in smaller quantities by the placenta and adrenal gland.

In addition to the maintenance of pregnancy, causes development of the mammary alveoli, enabling milk production, stimulates growth and secretory activity of the endometrial glands and inhibits myometrial, in the hypothalamus, reduces amplitude and frequency of basal gonadotropin releasing hormone (GnRH) secretory spikes, prevents the next estrous cycle, and inhibits the preovulatory LH surge.¹ The progesterone is used in treatment of the diseases with: pseudopregnancy, mammary tumours, benign prostatic hyperplasia, prostatic neoplasia, circum-anal adenoma, contracepcion and epilepsia.²

1.1. Pyometra

Canine pyometra is a disease affecting the adult intact bitch, causing a variety of clinical signs of genital and systemic disease. The concept of cystic endometrial hyperplasia (CEH) - pyometra - was introduced by Dow (1957)³ and stated that hormonal changes lead to CEH, which predisposes the uterus to secondary infection, leading to pyometra.⁴

1.1.1. Role of Progesterone in Pyometra

In dogs and cats, progesterone initiates endometrial hyperplasia by increasing the number and secretory function of the endometrial glands. When the secreted fluid accumulates in the uterine lumen, hydrometra or mucometra result. The abnormal uterus becomes infected, presumably via ascending bacteria from the vagina, causing pyometra.

Pyometra develops during the luteal phase of the cycle when progesterone concentrations are high, typically within 4–8 weeks of having been in heat. Endometrial hyperplasia can develop as a result of treatment with exogenous progestins. Exogenous estrogens (e.g., estradiol cypionate (ECP) for mismating) can also increase the risk of pyometra, presumably via their effects on progesterone receptors.¹

Clinical signs of pyometra include lethargy, anorexia, vomiting, and, in bitches, polydipsia/polyuria, purulent vulvar discharge is present in most, but not all cases. An enlarged uterus and dehydration are found on physical examination. Rectal temperature is usually normal or low. Fever is uncommon. Sepsis and shock often develop quickly.⁵

1.2. Feline Mammary Hyperplasia

Feline mammary hyperplasia represents a benign, progesterone-associated (occasionally develops in response to endogenous or exogenous progestins) fibroglandular proliferation of one or more mammary glands that may occur in both the female and male cat. It is also named feline hypertrophy, fibroadenomatous changes, or fibroadenoma complex or feline mammary fibroepithelial hyperplasia.⁶

1.2.1. Role of Progesterone in Feline Mammary Hyperplasia

The interaction between the activity of the mammary gland and the sex steroids is recognised for long. In brief, development and growth of the mammary gland is under the control of progesterone, which effects are mainly mediated through the progesterone receptor (PR) on stromal and epithelial cells. Local activation of PR triggers a cascade of specific and sequential series of molecules, specific for each glandular element, which stimulates mammary gland proliferation.⁷

Clinical signs is rapid, massive enlargement of all glands, which may outgrow the blood supply and begin to ulcerate. Tachycardia is found in some affected cats. Affected cats are usually otherwise healthy, although they may be quite thin, especially if they are also pregnant1.

2. Conclusions

Know the physiology of hormones involved in breeding dogs and cats is fundamentaal importance to the correct use and thus prevent diseases can also be caused by the same hormones.

Reference

1.  Johnson CA. Progesterone and prolactin-related disorders; adrenal dysfunction and sex hormones. In: Rand J, Behrend EN, Gunn-Moore D, Campbell-Ward ML, eds. Clinical Endocrinology of Companion Animals. Wiley-Blackwell; 2013:487–503.

2.  England GCW. Pharmacological control of reproduction in the dog and bitch. In: Simpson GM, England GCW, Harvey MJ, eds. Manual of Small Animal Reproduction and Neonatology. BSAVA; 2004;197–218.

3.  Dow C. The cystic hyperplasia-pyometra complex in the bitch. Vet Rec. 1957;69:1409–1415.

4.  Hagman R1, Kindahl H, Fransson BA, Bergström A, Holst BS, Lagerstedt AS. Differentiation between pyometra and cystic endometrial hyperplasia/mucometra in bitches by prostaglandin F2 alpha metabolite analysis. Theriogenology. 2006;66(2):198–206.

5.  Pretzer SD. Clinical presentation of canine pyometra and mucometra: a review. Theriogenology. 2008;70:359–363.

6.  Johnson C. Diseases of the mammary glands. In: Sherding R, ed. The Cat: Diseases and Clinical Management. 2nd ed. New York: Churchill Livingstone; 1994:1874–1875.

7.  Conneely OM, Mulac-Jericevic B, Lydon JP. Progesterone-dependent regulation of female reproductive activity by two distinct progesterone receptor isoforms. Steroids. 2003;68(10–13):771–778.