Lect 22

• The hypothalamic-pituitary-gonadal (HPG) axis is a crucial part of the reproductive system in animals.
• Prostaglandins are a type of biochemical structure.
• Cabergoline is a type of biochemical structure.
• eCG and hCG are types of biochemical structures.
• Acepromazine is a type of biochemical structure.
• Oxytocin is a type of biochemical structure.
• Melatonin is a type of biochemical structure.
• Corticosteroids are a type of biochemical structure.
• Peptides include GnRH and oxytocin, which are short chains of amino acids usually less than 20.
• Protein hormones include LH, FSH, prolactin, which are longer chains of amino acids.
• Steroids include estrogens, androgens, progesterone, which have a core of 4 carbon rings.
• Prostaglandins include PGF2 α and PGE, which are 20 carbon unsaturated fatty acids.
• Gonadotropin Releasing Hormone (GnRH) is a hypothalamic decapeptide that stimulates the release of gonadotropins (FSH, LH) from the anterior pituitary/adenohypophysis.
• Dopamine Agonists and Antagonists are used in the treatment of Parkinson's disease.
• Medroxyprogesterone acetate (MPA), megestrol acetate (MA), delmadinone, and altrenogest are examples of Progestins.
• Progesterone is produced by the corpus luteum (CL) and both progesterone and the Progestins, which are synthetic analogs, mimic the effects of the CL.
• Progestins act on progesterone receptors in the hypothalamus/pituitary, increasing the negative feedback and decreasing FSH and LH output.
• Steroids are synthesized from cholesterol and circulating steroids bind to and penetrate cell membranes of target cells, then bind to intracytoplasmic receptors, inducing nuclear production of mRNA, which codes for new protein synthesis by the target cell.
• Fescue toxicosis in mares is a condition caused by the consumption of fescue grass, which can lead to the induction of cyclicity in deep anestrous mares.
• The withdrawal of progestin therapy initiates a new estrous cycle and ovulation.
• Clinical applications of Progestins include supporting pregnancy, estrus suppression, suppression of libido in male dogs, and treatment of prostatic hyperplasia in dogs.
• The common molecular core of steroids is cyclopentanoperhydroperhydrophenanthrene, which consists of four carbon rings A, B, C and D.
• GnRH has a very short half-life (2-4 minutes).
• Clinical uses of GnRH include induction of ovulation or follicular luteinization and suppression of gonadotropin secretion (after a short period of stimulation; “flare-up” effect).
• Melatonin is not FDA-approved for oral or implant use.
• Clinical uses of Misoprostol and dinoprostone include cervical ripening, myometrial contractions, elective abortion, and tubal (oviductal) obstruction.
• PGF2 α is highly sensitive and should not be administered intravenously.
• Misoprostol (PGE1;$) and dinoprostone (PGE2;$$$) have actions of vasodilation and relaxation.
• Unfertilized oocytes become retained in the uterine tubes of mares and may form “oviductal masses” that may cause obstruction and infertility.
• Melatonin has clinical uses in inducing/suppressing the estrous cycles in seasonal breeders and treating atypical alopecia in dogs (Alopecia X).
• PGF2α has clinical uses in inducing luteolysis/abortion, controlling the estrous cycle, and treating pyometra (open-type).
• The male target tissue of Misoprostol and dinoprostone is penile tissues (erection).
• In farm animal species, PGF2α is synthesized in the uterine endometrium and released in late diestrus and at parturition, causing luteolysis (CL regression).
• The female target tissues of Misoprostol and dinoprostone are mature follicles, smooth muscle of uterine tubes, uterus and cervix.
• The action of PGF2α is luteolytic and causes the contraction of smooth muscle.
• PGF2α can facilitate semen collection by causing contraction of smooth muscle.
• Synthetic GnRH or long-acting GnRH analogs can be used.
• Synthesis strategy for GnRH analogs involves substitutions in aa positions 6 and 10.
• More than 2000 analogues of GnRH have been synthesized.
• Oxytocin is a nonapeptide synthesized in the hypothalamus and stored in the posterior pituitary.