Anterior Pituitary Hormones PDF

Anterior Pituitary Hormones Dr. Sovan Bagchi Professor of Physiology * www.gmu.ac.ae COLLEGE OF MEDICINE Anterior pituitary hormones Growth Hormone  Learni...

Anterior Pituitary Hormones Dr. Sovan Bagchi Professor of Physiology * www.gmu.ac.ae COLLEGE OF MEDICINE Anterior pituitary hormones Growth Hormone  Learning Objectives Describe growth hormone (GH) synthesis and sites of production Identify the cellular binding and major physiological actions of GH Describe the regulation of GH release by the anterior pituitary gland Describe prolactin synthesis and sites of production. Identify the cellular binding and major physiological actions of prolactin Describe the regulation of prolactin release Case BR is a 22-year-old college graduate who comes to see you for a physical. “Now that I have a job and my own health insurance, I thought I’d get a few things checked out. One thing might sound silly but I’m going to ask anyway. I’ve been really short all my life. You can’t imagine the bullying I got in middle school and high school. The only reason I was on the basketball team was that I was a quick defensive player. Last week, I was reading in a men’s magazine that there’s a hormone or a supplement that stimulates growth. That sounds like something I’d want to try. Would that work for me?” How would you counsel BR and what is the physiologic reason for your answer?  Growth hormone Growth hormone (GH; somatotropin) is a peptide hormone Plays important Role in bone growth GH is produced in the anterior pituitary gland by specialized cells called somatotrophs. It is structurally similar to prolactin  Transport and Receptor Binding IGF-1 is a member of a class of molecules known as somatomedins, molecules that are synthesized and secreted in response to GH and are responsible for mediating the actions and regulation of GH. The structure of IGF-1 is similar to insulin, hence its name. IGF-1 receptor binding produces many of the GH effects  Clinical correlation Clinically, IGF-1 is measured instead of GH when evaluating patients for a deficiency or excess of GH. This is because levels of IGF-1 are more stable than those of GH, which is released in a pulsatile manner during the day Growth Stimulation GH and IGF-1 act together to stimulate the growth of bones and muscles. They are jointly responsible for height IGF-1 has its greatest surge during puberty, when human growth is most rapid. IGF-1 can stimulate growth by signaling cells that adequate nutrients are available for them to undergo both hyperplasia and hypertrophy  Action of GH on Bones A great example of the combined action of GH and IGF-1 is the stimulation of linear bone growth at the epiphyseal plates in children. By age 18 (females) and 20 (males) the plate has closed and linear bone growth stops. Both GH and IGF-1 increase bone growth at the epiphyseal plate in children. On Muscles Both hormones also fuel skeletal muscle growth by stimulating myocyte hypertrophy and increasing protein synthesis Clinical correlation: Synthetic growth hormone (GH) is given to some children with short stature order to increase their height. But this has become controversial and has led to strict guidelines for use. GH is also taken by some athletes to increase muscle mass, but this use has been banned by most sports organizations Increasing Serum Glucose GH and IGF-1 also increase the serum glucose concentration Hepatic gluconeogenesis Lipolysis and lipid oxidation Antagonizing the action of insulin Just think! GH as a hormone that is trying to optimize your body for athletics: it increases blood sugar to build muscle and bone and increases lipolysis to reduce fat mass How Is Growth Hormone Regulated? Ghrelin During starvation, GH is secreted to maintain blood sugar This secretion is induced by another peptide hormone called ghrelin, secreted from the stomach Ghrelin is the main hormone that makes us hungry It is secreted by gastric cells before a meal to stimulate appetite and increase food intake; it works by acting on the hypothalamus, which is important in appetite control During periods of starvation, fasting, and weight loss, ghrelin is increased, and therefore so is GH Dwarfism Generalized deficiency of anterior pituitary hormone secretion A 10 yr. old child look like 4 to 5 yr. old - at age 20 yr. may have the bodily development 7 to 10 yr. Does not reach puberty as there is deficiency of gonadotropin. In 1/3 dwarfs only GH is deficient - do mature sexually and occasionally reproduce. In one type of dwarfism (Lévi-Lorain dwarf), GH secretion is normal or high, but inability to form somatomedin C Gigantism Excess GH secretion (e.g., Tumors in anterior pituitary at GH secreting center): before puberty Person can reach height up to 8 ft Hyperglycemia (over stimulation of pancreatic B cells and full- blown diabetes mellitus) Ultimately destruction of gland and deficiency of pituitary hormones - death in early adulthood Acromegaly Excess GH after puberty Person cannot grow taller. Bones of hands, feet, cranium, supra orbital ridges, nose continue to grow These growth leads to a person with protruded jaw, increased nose size,. Due to growth of vertebrae person become hunch backed clinically called kyphosis. Kidney, liver, tongue also greatly increased in size.  Test Your Knowledge! Which of the following sets of hormones is correctly paired with its site of secretion? A. GH: hypothalamus; ghrelin: pituitary B. GH: hypothalamus; somatostatin: liver C. GHRH: hypothalamus; ghrelin: pituitary D. GHRH: hypothalamus; IGF-1: liver E. GHRH: hypothalamus; somatostatin: stomach An injection of which of the following hormones would mostly likely increase the serum level of growth hormone? A. Ghrelin B. Glucose C. IGF1 D. Somatomedins E. Somatostatins Prolactin Learning Objectives Describe prolactin synthesis and sites of production Identify the cellular binding and major physiological actions of prolactin Describe the regulation of prolactin release  Prolactin is sometimes referred to as the “milk hormone” Regulatory roles in reproduction, nerve formation, and fetal development. Prolactin Prolactin is a peptide hormone produced It is structurally in the anterior similar to growth pituitary gland by hormone specialized cells called lactotrophs. Prolactin is also Produced in the produced by extra- anterior pituitary pituitary sites How Does Prolactin Act on Tissues? When released into systemic circulation, prolactin exerts its effects by binding to It also indirectly influences prolactin receptors in a the function of the gonads variety of tissues, including the breasts and the pituitary. Transport and Receptor Binding Physiologic Effects It enlarges and stimulates the mammary glands to produce milk Enhances maternal nurturing behaviors like cuddling, protection, and grooming.  It depresses sex hormones Prolactin Inhibits GnRH Inhibits FSH and LH As a result, the gonads produce less estrogen in women and less testosterone in men Immune Effects Prolactin suppresses the This may be a mechanism negative selection of B for the higher incidence of cells, making the immune autoimmune diseases in system more likely to women of childbearing age attack native cells and in postpartum women (autoimmunity) How Is Prolactin Secretion Regulated? Positive regulators Nipple stimulation Estrogen Thyrotropin-releasing hormone Negative Regulator Dopamine Circulating prolactin signals the hypothalamus to increase production of dopamine. In turn in turn inhibits prolactin secretion Prolactin secretion is regulated Progesterone inhibits prolactin at the level of the peripheral receptor. Clinical correlation The effect of dopamine on prolactin is clinically important when we prescribe drugs that increase dopamine levels, such as amphetamines; drugs that reduce dopamine levels, such as antipsychotics, including chlorpromazine; or drugs for mood disorders, such as risperidone Prolactin in Pregnancy Prolactin is made at high levels at a steady state in pregnancy and during nursing. The combination of continuous, high-level production of prolactin and its continuous inhibition by dopamine results in a stable basal level of serum prolactin as well as a significant prolactin “reservoir.” This means that under the right stimulatory conditions (like nursing), the anterior pituitary is able to secrete a high concentration of prolactin into the bloodstream, achieving peak prolactin levels quickly when needed Test your knowledge! Which of the following hormones Which of the following decreases increases during pregnancy and directly prolactin secretion? increases prolactin production? Dopamine Estrogen Estrogen Follicle-stimulating hormone Nipple stimulation Gonadotropin-releasing hormone Sight of a crying infant Progesterone Thyrotropin-releasing hormone Thyrotropin-releasing hormone Learning Resources Textbook: John E. Hall and Michael E. Hall. Textbook of Medical Physiology. 14th ed. Elsevier. 2021. ISBN: 978-0-323-59712-8. Chapter 76, Page no. 929-940 Power-point presentation in the moodle