What is LH (luteinizing hormone) and when is it released? (Canine)

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What is LH (luteinizing hormone) & when is it released? (Canine)

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Luteinizing hormone is a protein hormone that is released from a part of the brain, called the pituitary. LH is released in an episodic manner (in short bursts) after stimulation from another master hormone (gonadotropin releasing hormone or GnRH for short) in response to all sorts of cues such as- Environmental cues like: daylight length, rainfall and temperature. Social cues: like presence of a mate or other cycling females and/or Physiologic cues: like attaining a certain body size supportive of reproduction. When LH is released into the bloodstream, it creates effects on distant tissues like the gonads (testes in males, and ovaries in females) to trigger the production and release of other important hormones. These hormones, in turn, by their level of production send signals back to the brain for either increased or decreased release of LH. Like a worker on the floor of the factory sending a signal to the foreman to speed up or slow down the delivery of raw materials to be manufactured into a product.

What does LH do in the (queen) female dog?

LH is the initial signal sent from the pituitary to signal the release of hormones that will result in ovulation of multiple follicles (where the eggs are held in the ovary). Picture from Senger 2-11 and 8-2. It normally occurs 36-48 hours ahead of ovulation in the queen. It is also responsible for the early development of the corpus luteum- the structure that develops in the ovary after ovulation of a follicle, that will produce and secrete progesterone in quantities capable of maintaining a pregnancy. Senger 9-8 In the dog, it is felt that LH is one of the 2 main hormones active in maintenance of the luteal bodies during pregnancy as drugs that disrupt the production of LH will inevitably cause pregnancy failure and loss of the luteal bodies. Prolactin is the other main hormone thought to assist in luteal maintenance in the dog.

What does a high level of LH indicate?

There are 3 possibilities for this result:

1: This is an intact female experiencing the pre-ovulatory LH rise that will result in ovulation hours to days later.

2: This is a spayed female which does not have enough estrogen or progesterone from her ovaries to suppress release of LH from the pituitary (foreman keeps sending out more raw materials because he can't hear the workers telling him to stop)

3: The ovary has a type of tumor that is interfering with LH hormone receptors causing sustained release of LH from the pituitary as the pituitary assumes the signal has not been received.

Other medical history, diagnostic tests and clinical findings can be used to sort these out.

What do you normally use LH for?

LH is an extremely helpful hormonal result to have when planning a breeding. Especially in the case of timed breedings such as limited access to one of the breeding pair, shipment of frozen or cooled sperm, subfertility of one or both of the breeding pair, optimal timing of the breeding is key. Breeding at the point in time when eggs are ready to be fertilized and sperm is at its peak fertility, can ensure success and maximize chance and rate of fertility. Once identified, typically the ideal time window for planned breeding is 4-6 days post LH peak.

Because the length of gestation is typically 65 days post LH peak, time of whelping can also be estimated from this data, and this can helpful in making decisions when to take time off of work to be home to observe the bitch/queen and can also be used to increase safety in surgical intervention such as in a C-section. We also use this information to plan elective C-sections for breeds that are known for difficult birthing e.g. the English bulldog.

LH can also be used to identify spayed/neutered animals. As LH will be persistently elevated about 2 weeks after gonads are removed, this can be helpful in identifying a stray or found animal as spayed/neutered without the need for surgery, identification of retained gonadal tissue (cryptorchid males and ovarian remnant syndrome in females), potentially also for identification of a granulose-thecal cell tumor of the ovaries in some bitches and bitches with testicular/ovarian failure such as intersex conditions or toxic injury to the gonads.

How often do you need to check serum for LH?

As LH is released in an episodic manner (short burst over seconds) in response to multiple GnRH pulses, LH is normally only elevated fro a short period of time. Usually only 12-24 hours. There are a few bitches that may have LH pulses that are shorter over even longer than this. If the LH pulse was too short to catch ona asingle test, we use progesterone tests to estimate the approximate time of LH surge and future ovulation. If the LH surge is long i.e. greater than 36 hours, then we usually estimate the fertile period from the day of the last test that was positive for the surge. In every case, we need to be able to identify when LH was high (positive test) and low (negative test) to make the result meaningful. This means running a minimum of 2 tests and perhaps many more. In cases where progesterone is concurrently being used, we have the option of saving serum frozen and testing samples retrospectively (days after they were drawn) to identify the LH peak to use in ovulation timing.

In case of identification of retained or functionally active gonadal tissue, more than one test may be needed depending on the animals' history and other clinical findings. Dr Sebzda can consult with you regarding your pet's case to determine what is expected in the individual situation.

How is LH tested?

LH assays come in semi-quanttiative enzyme linked absorbent assays (ELISA) kits from Synbiotics. The LH test requires about 40 minutes for sample preparation and another 20 minutes for analysis. Not to worry though, you may always just have the pet come in for one of our experienced and caring technicians to draw the blood sample and have Dr Sebzda call you with the results at home (or any other contact info you provide), lessening the length of time you need to wait in the hospital.

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