How hormones work during heat cycle of a cat

Since in our article series about cats in heat we mention different hormones a lot, today we are going to explain some basic stuff about hormonal activity during heat cycle of a female cat.

The heat cycle begins with a phase named proestrus and is initiated by Follicle-stimulating hormone (FSH) which is released by the pituitary gland in the brain of a cat. FSH, as its name suggests, stimulates the growth of egg follicles in the ovaries of a cat.

Newly formed eggs begin to produce another hormone, called estrogen. As its levels rise, the cat enters the second phase of the heat cycle, which is estrus.

Estrogen is usually called as female hormone and is responsible form most behavior changes of the cat during the heat cycle. By now, your cat will start screaming, rolling on the floor and showing other symptoms of heat.

From the reproductive standpoint, main functions of estrogen is to prepare eggs to be released, as well as thickening of the uterine lining, so it becomes receptive.

Estrogen stays high for three to four days and then falls abruptly, signaling the end of the heat cycle. If the cat didn’t mate, she will enter a phase named interestrus, which will lead to another heat cycle shortly.

If, however, the mating did happen, vaginal stimulations induce the secretion of Luteinizing Hormone (LH), which in turn causes ovulation within one, maximum two days of the mating, or series of matings.

Cats are induced ovulators, which means, eggs will not be released if copulation does not occur. Interesting enough, ovulation may be induced not only by mating, but by mechanical stimulation, as well. IMPORTANT, mechanical stimulation is a procedure done in veterinary setup. Trying it at home may lead to severe injury of your cat’s reproductive system.

LH is not only responsible for ovulation, but also initiates the production of progesterone.

Progesterone is a hormone which main functions are to support implantation and pregnancy maintaining. Progesterone peaks at about 20 days after the intercourse in both pregnant and non pregnant cats.

If the cat is not pregnant (exhibits false pregnancy), progesterone will drop gradually during the next 20 days and will get back to normal cycling again, producing FSH and estrogen again. The cat may show some signs of “real” pregnancy.

If the cat is pregnant, progesterone will stay at high levels (lower than the peak level) for 20 more days and then, will decrease gradually during the last 20 days of pregnancy.

During winter, as the amount of light decreases, another hormone Melatonin is produced in amounts higher than usual, which suppresses the production of FSH and LH, therefore, the cat enters anestrus, which means – cat won’t go in heat during the winter.

In the future of series about cats in heat, we will talk about symptoms of a cat in heat and other ways to tell whether your cat is in heat.