pit9

Overview:posterior pituitary hormones
- Oxytocin
- Vasopressin
- Synthesis Site:
  - hypothalamus ® posterior pituitary ®stored ®released

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Oxytocin:Overview
- Levels:
  - physiologic levels:cause milk ejection in lactating women
  - pharmacological doses:
    - induce uterine contraction/maintain labor
- Chemistry:oxytocin
  - 9-amino acid peptide
- Pharmacokinetics: oxytocin
  - IV administration for labor stimulation
  - nasal spray: postpartum lactation induction
  - catabolism: renal & hepatic
  - half-life: (circulating) 5 min.
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- Pharmacodynamics: oxytocin
  - influences ionic currents in myometrial smooth muscle ® uterine contraction
  - uterine sensitivity to oxytocin: increases in pregnancy
  - inhibition of oxytocin-induced myometrial uterine contraction:
    - magnesium sulfate
    - b-adrenergic receptor agonists
    - inhalation anesthetics
  - promotes myoepithelial cell contraction (surrounding mammary alveolar) ® milk ejection
  - normal lactation requires oxytocin
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- Clinical Uses:oxytocin
  - Diagnostic Applications:oxytocin
    - Checking placental circulatory reserve:
      - IV oxytocin near-term ®uterine contractions ®decrease fetal blood supply® fetal heart rate response monitored (abnormal response may suggest intrauterine growth retardation; may suggest advisability of cesarean section
  - Therapeutic Uses:oxytocin
    - labor induction
    - promoting dysfunctional labor
      1. when early vaginal delivery is required
        
        Rh factor concerns, maternal diabetes, preeclampsia
      2. uterine inertia
      3. incomplete abortion
    - control of postpartum uterine bleeding
    - enhance impaired milk ejection (nasal Route of Administration)
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- Toxicity:oxytocin
  - serious toxicity: rare
  - reported adverse reactions include: hypertensive reactions, uterine rupture, water intoxication, fetal death, afibrinogenemia
- Contraindications:oxytocin
  - fetal distress, abnormal fetal presentations, factors predisposing to uterine rupture

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Vasopressin:Overview:
- peptide hormone
- released by posterior pituitary in reaction to:
  - rising plasma tonicity
  - decreasing blood pressure
- antidiuretic properties
- vasopressor properties
- vasopressin deficiency: ® diabetes insipidus
Structure:vasopressin
- nonapeptide
Pharmacokinetics:vasopressin
- Routes of administration:
  - IV, intramuscular, intranasal
- half-life: 20 minutes
- Renal & hepatic catabolism
- minimal vasopressin excreted unchanged in the urine
Pharmacodynamics:vasopressin
- Receptor types:
  - V₁-- vascular smooth muscle (vasoconstriction)
  - V₂ -- renal tubule cells: antidiuresis
    - Mechanism: (1) increased water permeability and (2) increased collecting tubule water resorption
  - extrarenal V₂ receptors--promote coagulation factor VIII_c and von Willebrand factor release.
- Desmopressin acetate (DDAVP, 1-desamino-8-D-arginine vasopressin)
  - synthetic vasopressin derivative
  - long-acting
  - limited V₁receptor activity
  - significant antidiuretic/vasopressor ratio compared to vasopressin (4000: 1)
Clinical Use:vasopressin
- Vasopressin & desmopressin: alternative treatment for pituitary diabetes insipidus
- Nocturnal enuresis (desmopressin at bedtime) -- mechanism: reduced night urine production
- IV vasopressin: may be effective in managing esophageal variceal bleeding and colonic diverticular leading
Toxicity:
- Vasopressin (not desmopressin): vasoconstriction -- cause issues in patients with coronary vascular disease
- Unusual side effects include: agitation, allergic reactions, abdominal cramping, headache, nausea