THE HORMONE PAGE

Activin - Activin is a beta-beta homodimer with a MW of approximately 24,000; activin is suspected to over-ride the inhibitory effect of inhibin on FSH secretion

Adrenocorticotrophic Hormone (ACTH) - ACTH is peptide released from the corticotrope cells of the anterior pituitary: ACTH stimulates the release of cortisol from the adrenal cortex; corticotropin-releasing hormone (CRH) from the hypothalamus stimulates ACTH release from the anterior pituitary

Aldosterone - a steroid from the adrenal cortex, aldosterone is the principal mineralocorticoid; aldosterone promotes Na⁺ retention at the kidney in exchange for secretion of K⁺

Androgens - generally thought of as the "male" gonadal steroids, androgens also serve as precursors for production of estrogens in female (see the 2 cell hypothesis in the notes); an example of an androgen is testosterone; androgens are produced by theca cells in the ovary and Leydig (interstitial) cells in the testis

Androstenedione - this androgen metabolite continues to be produced at low levelsy by the ovarian stroma following menopause

Angiotensin I and II (ANG I & II) -

Angiotensinogen - this protein precursor molecule is produced by the liver and circulates in plasma; renin from the kidney cleaves angiotensin I (ANG I) from angiotensinogen; ANG I is then converted to ANG II by angiotensin converting enzyme in the lungs

Antidiuretic hormone (ADH) - this peptide, released from the posterior pituitary in response to increased plasma osmolarity, promotes water reabsorption by opening water channels in the distal convoluted tubule and collecting ducts of the kidney, leading to the production of a more concentrated urine; ADH is actually synthesized in the hypothalamus and transported to the posterior pituitary for storage and secreted from the posterior pituitary as required

Calcitonin - a peptide hormone with 32 amino acids produced by the parafollicular cells of the thyroid; calcitonin opposes short term effects of PTH on plasma Ca²⁺; calcitonin quickly decreases osteoclast function to slow demineralization of bone and so has been used in the treatment of persons with osteoporosis

Cortisol - a steroid from the adrenal cortex, cortisol is the principle glucocorticoid (GC); GC's oppose the effect of insulin on plasma glucose levels (ie. cortisol prevents baseline plasma glucose from falling to levels that would be considered hypoglycemic)

Corticotropin Releasing Hormone (CRH) - this tiny hypothalamic peptide gains access to the anterior pituitary via the pituitary portal system; at the pituitary, CRH stimulates synthesis and release of ACTH

Endogenous Opioid Peptides (EOP's/opioids) - small peptides produced by the body which have opiate like activity; eg. endorphins, enkephalins, kytorphins, dermorphins, dynorphins and others; while these opioids appear to have natural pain killing properties, they also suppress reproductive activity in females during childhood, during periods when progesterone is elevated (luteal phase, pregnancy), or in some instances where stress or low body fat composition interfere with the function of the adult reproductive axis

Estrogens - typically thought of as the principal bioactive gonadal steroid of the non-pregnant female during the follicular (proliferation) phase

Follicle Stimulating Hormone (FSH) - a glycoprotein with a molecular weight of approximately 33,000 produced by "gonadotrope" cells of the anterior pituitary; FSH release is stimulated by GnRH; FSH has a circulating half-life of approximately 2.5 hours; FSH has an alpha and beta subunit, each making up about 50% of the hormone by mass; the alpha subunit is identical to the alpha subunit of LH, hCG and TSH; thus, the beta subunit of FSH imparts hormone specificity

GHRH - growth hormone releasing hormone is released from the hypothalamus and stimulates GH secretion from the somatotrope cells of the anterior pituitary

Glucagon - this polypeptide hormone is produced by the alpha cells of the pancreas; glucagon is composed of a string of 29 amino acids; glucagon works with cortisol to oppose the effects of insulin; that is, glucagon and cortisol (the principle GC) prevent basal plasma glucose levels from falling too low between meals

Gonadal Steroids - see androgens, estrogens, progestagens

Gonadotropins - see LH, FSH and hCG; gonadotropins are glycoproteins which are stimulatory to steroid production and other activities of the gonads

Gonadotropin Releasing Hormone (GnRH) - a decapeptide (meaning a strand of 10 amino acids) with a molecular weight around 1200;  this tiny hypothalamic peptide has a circulating half-life measured as less than 10 minutes;  released into the hypothalamic pituitary-portal system in small quantities contained in short, discrete pulses, this hormone is impossible to measure directly on a clinical basis (see luteinizing hormone)

Granulopoietin - a glycoprotein hormone produced by macrophages; granulopoietin stimulates the production of the granulocytic series cells (neutrophils, eosinophils and basophils)

Growth Hormone (GH) - a 191 amino acid polypeptide hormone produced by somatotropes in the anterior pituitary; growth hormone stimulates the synthesis and activity of the somatomedins (insulin-like growth factors); somatomedins (IGF's) are hormones produced by target tissues which actually cause growth of the target tissues; in other words, GH does not directly make tissue grow but, rather, increases IGF production which makes tissues grow

Human Chorionic Gonadotropin (hCG) - a glycoprotein produced by the syncytiotrophoblast cells (fetal component) of the placenta; hCG has a molecular weight of approximately 37,000.  hCG has 2 subunits, the alpha subunit being slightly smaller; the alpha subunit is identical to the alpha subunit of LH, FSH and TSH; the beta subunit imparts hormone specificity

Human Chorionic Somatomammotropin (hCS) - also known as placental lactogen (hPL); this hormone is produced by the chorion of the placenta and acts as the fetal growth hormone

Human Placental Lactogen (hPL) - see human chorionic somatomammotropin

Inhibin - Inhibin is an alpha-beta heterodimer with a MW of approximately 32,000;  Inhibin specifically suppresses synthesis and secretion of FSH by the pituitary

Insulin - is a dipeptide (2 peptides linked by 2 disulfide bridges) produced by beta cells of the pancreatic islets; insulin is released by a number of gut peptides which are released into the bloodstream as glucose is absorbed across the gut wall (which is why the glucose tolerance test is given orally); insulin has a circulating half-life of approximately 4 minutes and a molecular weight of around 6000

Luteinizing hormone (LH) - a glycoprotein with a molecular weight of approximately 30,000 produced by "gonadotrope" cells of the anterior pituitary; LH release is stimulated by GnRH; LH is released in distinct and easily measured pulses in the bloodstream; LH pulses reflect GnRH pulses; LH has a circulating half-life of approximately 25 minutes; LH has an alpha and beta subunit, each making up about 50% of the hormone by mass; the alpha subunit is identical to the alpha subunit of FSH, hCG and TSH; thus, the beta subunit of LH imparts hormone specificity

Melanocyte Stimulating Hormone (MSH) - Along with the peptides Beta-endorphin, and ACTH, MSH is a peptide cleaved from the precursor polypeptide "pro-opiomelanocortin."  MSH stimulates melanocytes to produce the protective brown pigment melanin (absorbs potentially harmful UV rays).

Oxytocin - a peptide released from the posterior pituitary, oxytocin is an important mediator the "milk letdown reflex."  Like ADH, oxytocin is actually synthesized in the hypothalamus and transported to the posterior pituitary for storage and then secreted from the posterior pituitary as required.  Thus, while synthesized in the hypothalamus, oxytocin and ADH are known as the "posterior pituitary hormones," as they are released from the posterior pituitary.

Parathyroid hormone (PTH) - a straight chain peptide with 84 amino acids; PTH generally elevates plasma Ca²⁺ levels to keep Ca²⁺ within the normal range

Prolactin (prl/prol) - together with estrogens, progestagens, GH, glucocorticoids and hPL, prolactin promotes mammogenesis in preparation for milk production; milk secretion following parturition is associated with further enlargement of the lobules and milk synthesis and requires PRL, insulin and the adrenal steroids

ProstaglandinF_2alpha - produced by the ovary in women, it is the suspected luteolytic factor

Prostaglandins (PG's) - these are fatty acid metabolites made from arachadonic acid; prostaglandins are implicated in many activities in the body; there are multiple families of prostaglandins, some having effects that are opposite to one another; PG's of the F family are thought to be luteolytic and vasoconstrictors, while PG's of the E family are thought to be luteotropic and vasodilators.  Prostaglandins are also used as pain transmitters... aspirin suppresses prostaglandin synthesis by the cyclo-oxygenase pathway.

Relaxin - a protein produced by the corpus luteum verum which leads to relaxation of the pelvic ligaments and other connective tissues in preparation for the birth process

Renin - an enzyme released by the juxtamedullary apparatus of the kidney; renin released angiotensin I (ANG I) from the circulating precursor molecule, angiotensinogen; ANG I is then converted to ANG II by ANG converting enzyme in the lung

Somatostatin - this protein hormone is produced by the hypothalamus and the delta cells of the pancreatic islets; somatostatin inhibits the release of GH and is sometimes referred to as "growth hormone inhibiting hormone," or GHIH; we used to think if we could immunize against somatostatin, we could make cattle grow faster - it proved easier to treat with GH's and anabolic steroids!

TSH - thyroid stimulating hormone; also known as thyrotropin; released from thyrotrope cells of tthe anterior pituitary, TSH stimulates synthesis and release of T3 and T4 from the thyroid gland; a glycoprotein composed of an alpha and beta subunit, TSH has the same alpha subunit as LH, FSH, and hCG

TRH - a peptide composed of only 3 amino acids; thyrotropin releasing hormone is released from the hypothalamus and stimulates the release of TSH from thyrotrope cells of the anterior pituitary