posterior pituitary gland and hormones

structure of oxytocin and arginine vasopressin on amino acid level

• 9 amino acid long peptides

• oxytocin

  • contains ile and leu

• (arginine) vasopressin

  • contains phe and arg

neurophysins

• released in conjunction with the active hormone

• from cleaves pre hormone

what are the physiological effects of oxytocin?

1. stimulation of milk ejection

2. stimulation of uterine smooth muscle contraction at birth

3. establishment of maternal behaviour

stimulation of milk ejection

• oxytocin binds to myoepithelial cells near the alveoli

• calcium release causes these cells to contract

• milk ejects

suppression of milk ejection

• fear anxiety pain and alcohol will inhibit the release of oxytocin

• catecholamines released from adrenal gland

• sex steroids reduce production of and response to oxytocin

  • burst of oxytocin is triggered by declining of progesterone after childbirth

stimulation of uterine smooth muscle contraction at birth

• inc expression of oxytocin receptors on uterine smooth muscle during later stages of gestation

• fetus exerts pressure on cervix, activation of sensory nerves, oxytocin released

synthetic oxytocin pros and cons

• pros can be used to further stimulate contractions , inhibitors can be used to prevent premature labour 

• cons more monitoring bc hyperstimulation can cause reduced blood flow to baby causing brain damage, cerebral palsy, uterine rupture and low heart rate 

establishment of maternal behaviour from oxytocin

1. infusion of oxytocin into brains of virgin rats rapidly induce maternal behaviours

2. administration of antibodies or antagonists to oxytocin will stop them from showing positive maternal behaviours

3. mice with disruptions of oxytocin gene disruption show normal maternal behaviour but deficits in milk ejection

   1. oxytocin is a major facilitator but not absolute initiator

oxytocin in males

• helps facilitate sperm transport

• social behaviour impacts - survival, security and sociability

  • depends on context and surroundings

vasopressin function

• stimulates synthesis and insertion of aquaporins

• inc osmolality of urine

control of vasopressin

• inc osmolality is detected by hypothalamic osmoreceptors

• aortic arch, left atrim and carotid sinus baroreceptors detect a drop in blood volume and stimulate vasopressin release

when is vasopressin suppressed or decreased

• when plasma osmolality falls then vasopressin is suppressed

• dec by ethyl alcohol, caffeine (dehydration and hangover)

when is vasopressin secretion increased

• angiotensin

• pain

• trauma

• anxiety 

• nausea 

• vomiting

• blood loss

• drugs - nicotine, morphine 

secondary effects of vasopressin

• memory formation and learning

• anti fever and pain relief

• aggression towards strangers and intruders in territory

three types of diabetes insipidus

1. hypothalamic

2. nephrogenic

3. psychogenic

hypothalamic diabetes insipidus 

• deficiency in vasopressin secretion

• caused by head trauma infections or tumours involving the hypothalamus

nephrogenic diabetes insipidus

• kidney is insensitive to vasopressin

• caused by renal disease, mutations in vasopressin receptor gene or gene encoding aquaporin 2

psychogenic diabetes insipidus

• compulsive water drinkers

• if water is witheld, the adh secretion increases, urine decreases

ADH binds to which vasopressin receptor for aquaporin insertion

• vasopressin-2 receptor

• GS - cAMP - PKA pathway 

ADH effect during vasodilatory shock

• ADH binds to V1 receptor on vascular smooth muscle

• G1 signalling pathwau

• stimulates contraction

syndrome of inappropriate secretion of ADH

• dec serum osmolality does not inhibit ADH secretion

• water is retained bc ADH is too high

• inc blood pressure

• low sodium in blood