Pituitary Gland Hormones

Posterior Pituitary Gland (Neurohypophysis)

  • Does not produce its own hormones; it releases hormones made in the hypothalamus.
  • Hormones:
    • Antidiuretic Hormone (ADH) / Vasopressin: Involved in antidiuretic effects.
    • Oxytocin

Anterior Pituitary Gland

  • Lactogen / Prolactin: Affects breast tissue.
  • Gonadotropic Hormones: Affect ovaries and testes, leading to the release of oestrogen, progesterone, and testosterone.
  • ACTH / Corticotropin: Affects the adrenal cortex, leading to the release of cortisol and aldosterone.
  • Thyrotropin: Impacts the thyroid, which produces T4 and T3, commonly associated with metabolism and metabolic rate.
  • Growth Hormone / Somatotropin: Influences many organs of the body.
  • Endorphins: Affect diverse organs and tissues, associated with a feeling of well-being during exercise.

Growth Hormone

  • The hypothalamus secretes Growth Hormone Releasing Hormone (GHRH) or Growth Hormone Inhibiting Hormone (GHIH) / Somatostatin depending on the body's needs (feedback loop).
  • Anterior pituitary releases growth hormone.
    • Direct Actions:
      • Anti-insulin effect on adipose tissue causing the release of triglycerols, which can be used as an energy source.
      • Inhibits glucose uptake to maintain blood sugar levels.
    • Indirect Actions:
      • Primarily promote anabolism.
      • Act on the liver and other organs via somatomedins.
        • Non-skeletal effects: New protein and cell growth.
        • Skeletal effects: Increases cartilage formation and promotes skeletal growth.
  • Feedback Control:
    • Stimulation or inhibition of growth hormone release via GHRH or GHIH.
    • Inhibition of growth hormone synthesis.
  • Growth hormone interacts with the cell membrane via JAK proteins.

Growth Hormone Forms

  • Monomeric, dimeric, oligomers, and fragments.
  • Different sizes: 22 kDa, 20 kDa, 30 kDa fragments, etc.
  • Free or bound forms.

Growth Hormone & Training

  • Lynn Mano study (2006) used bilateral leg extension exercise:
    • Submaximal loading: 5 sets of 10 at 70% of 1RM.
    • Maximal explosive resistance exercise loading: 5 sets of 10 at 40% of 1RM.
    • Heavy Resistance Training: 5 sets of "proper" 10RM.
    • Results: The growth hormone response was greatest in the heavy resistance training condition and lowest for the submaximal loading condition.
    • Highest growth hormone responses occurred in the program with the highest lactate values, indicating a relationship between lactate and growth hormone release.
  • There are strong correlations between the increase in lactate and corresponding increases in growth hormone. Bouts of exercise that stimulate large amounts of lactate formation (compound exercises, moderate to high volume, and high intensity programs), may be conducive to growth hormone release.
  • High volume, high intensity workouts with short rest periods, compound exercises, and Olympic weight lifting show the highest growth hormone release.
  • Acute hormonal responses and training outcomes:
    • Hormone levels spike immediately after exercise but return to baseline quickly (within 15-30 minutes).
    • Hormones might kick-start processes that continue after initial spike, like muscle protein synthesis which lasts about 48 hours.
  • There is no direct correlation between the amount of growth hormone released after exercise and the amount of hypertrophy observed after a training program.

Insulin-Like Growth Factor (IGF)

  • Structurally related to insulin; may mediate many actions of growth hormone.
  • Small polypeptide hormones:
    • IGF-1: ~70 amino acids.
    • IGF-2: ~67 amino acids.
  • Produced in the liver in response to growth hormone-stimulated DNA synthesis.
  • IGF-1 interacts with its own receptors but can have some cross-reactivity with other receptors.

Roles of Insulin & IGF

  • Insulin may have metabolic actions.
  • IGF-1 might help with growth, differentiation, cell proliferation, and survival.
  • IGF-2 might work towards IGF clearance, cell mitigation, and calcium influx.

Acute Responses

  • The type of resistance training program impacts the IGF response.
  • Larger IGF increase with strength-power type programs compared to hypertrophy programs.
  • These studies can be affected by the training status of the athlete, age, biological sex, and nutrition.
  • IGF-1 secretion may be delayed until it is stimulated by growth hormone.

Research

  • Bannmann et al. examined the effects of Smith machine squats on IGF (eccentric and concentric loading):
    • Both loading paradigms resulted in IGF release.
    • There was no difference between the concentric and eccentric loading groups but there were some differences to baseline being pre exercise.
  • Carly et al. (2020) study:
    • Healthy young men were divided into endurance athletes, strength athletes, or non-training control participants.
    • There is thought to be a decrease in IGF-1 with overreaching.
    • Results: A statistically significant reduction of glucose concentration and the highest expression of IGF-1 in athletes suggests the anabolic effect of IGF-1 through insulin receptors on many tissues under the influence of moderate physical exercises, mainly during resistance training.
    • IGF response to exercise is greater in athletes, and endurance or strength trained people, see very similar increases.